For close to four decades before cellular service opened in the United States, a telephone in a vehicle meant sharing a radio channel with every other subscriber in the city. The call usually went through an operator, and in large cities the service was often available only after years on a carrier’s waiting list. This piece covers the Bell System’s Mobile Telephone Service from 1946, the Improved Mobile Telephone Service that followed in the 1960s, the channel shortage that limited both, and the engineering change AMPS cellular made in 1983. It closes on why that history left public safety treating its own radio system as the only link it could count on.

St. Louis, June 17, 1946: what Mobile Telephone Service actually sold

AT&T’s published corporate history dates the start of commercial Mobile Telephone Service, usually shortened to MTS, to June 17, 1946. On that date Southwestern Bell put the service into operation in St. Louis. The date and the city are well documented, and they are the ones I use. The early customers were mostly businesses with vehicles on the road. The vehicle equipment was large enough that it usually went in the trunk, with only a control head and handset in the cab.

In radio terms, MTS used a single high-power base station on a tall site to cover a metropolitan area. It talked to mobile units that also ran at substantial power, on FM channels in the VHF spectrum. The base station connected to the public telephone network through a mobile service operator at a switchboard, so every call in either direction passed through a person. Accounts of the St. Louis opening describe a small number of channels in the 150 MHz range. Some add that interference between adjacent channels left fewer of them usable than were licensed. I have not found a primary engineering document for the opening configuration, so I will not give a single channel count for St. Louis in 1946, and I would treat any precise figure you see as secondhand.

The Bell companies extended MTS to other cities over the following years. The basic design stayed the same: a single large site, with an operator connecting each call. For readers who work radio, the closest modern comparison is a conventional base station with a phone patch, which is essentially what a subscriber was renting. The important difference is that the subscriber shared the channel with strangers rather than with a dispatcher and a fleet. That difference drives most of the rest of this history, because strangers could not be told to stay off the air when someone needed the channel.

Push to talk and ask the operator: how an MTS call worked

MTS was half duplex. The subscriber held a push-to-talk button to speak and released it to listen, exactly as on a dispatch radio. To place a call, the subscriber first monitored the channel. If it was quiet, they keyed up and asked the mobile operator for the number they wanted. The operator dialed it on the landline side and kept track of the call for billing. If the channel was busy, the subscriber could try another channel in the service area if the radio had one and it happened to be free. Otherwise the only choice was to wait.

A call to a vehicle went the other way through the same operator. The landline caller asked for the mobile service, the operator signaled the vehicle over the radio channel, and the subscriber answered by keying up. The person on the landline side could not be heard while the mobile was transmitting, so ordinary telephone users had to learn to take turns, a habit dispatchers and field units already had. An MTS call also could never move faster than the operator queue at the switchboard. The switchboard tended to be busiest during the same periods when the radio channel was congested.

MTS offered no privacy. Every other subscriber monitoring the channel while waiting for it to clear could hear both sides of the conversation, and so could anyone with a receiver tuned to the frequency. An open channel like that suited short logistical calls far better than anything confidential. That is roughly the use public safety later made of the phone patch on its own systems, where a patch was the occasional exception and voice dispatch on the agency channel remained the routine.

For the subscriber, the experience combined the inconveniences of radio and telephone. They needed a free channel and a free operator, and they had to accept that the call was public. The convenience they were paying for was reaching the telephone network from a moving vehicle at all. For a business with trucks on the road in the late 1940s, that was worth a good deal, even on those terms.

A handful of channels per city: where the waiting lists came from

Each MTS channel, and later each IMTS channel, carried one conversation at a time across the whole coverage area, so a city’s capacity was simply its number of channels. Several reasons combined to keep that number small. The VHF spectrum where mobile telephone operated was shared with police, fire, taxicab, utility and other land mobile users, all of them growing after the war. Channels in the 1940s were wide by later standards, because the transmitters and receivers of the period needed generous spacing to stay clear of their neighbors. The base stations also ran high power from tall sites, so a channel used in one city could not be reused in a nearby one without interference. That meant the same few frequencies could not be packed densely across a region.

The channels that did exist were split between two kinds of carrier. By the end of the 1940s, the FCC had divided mobile telephone channels between the wireline telephone companies and independent radio common carriers. The independent carriers built competing services in many cities and often ran paging as well. That division between wireline and non-wireline carriers carried forward into the cellular licensing of the early 1980s. It is why every early cellular market had one license reserved for the local telephone company and one for another company.

Once the channel count was fixed, the only way a carrier could keep service usable was to limit the number of subscribers. With a few channels and a few hundred customers, the chance of finding every channel busy during the business day was already high, and each added subscriber made it worse for everyone. Carriers therefore kept waiting lists, and in the largest cities the wait for service is commonly described as running to years.

The figure most often repeated comes from the Bell System’s New York service in 1976: about a dozen channels, a little over 540 subscribers and roughly 3,700 people on the waiting list. It appears in many histories, with the subscriber count given as 543 in some and 545 in others, and I have not traced it to a primary Bell System document. I treat it as approximately right. Its scale fits what the channel math predicts for a metropolitan area served by about a dozen channels, each carrying a single call.

IMTS from the mid-1960s: dialing, full duplex and the same ceiling

The Bell System began offering the Improved Mobile Telephone Service in the mid-1960s, and most histories give 1964 as the year of introduction. IMTS fixed the parts of MTS that subscribers found most awkward. It was full duplex, with separate transmit and receive frequencies so both parties could talk at once as on a wireline phone. The subscriber could also dial local calls directly from the vehicle without an operator, and landline callers could dial a vehicle’s own number.

The change that matters most to a radio administrator is automatic channel selection. The base station marked an idle channel with a tone. The mobile scanned the channels in its band and locked onto the marked one, and the subscriber’s identity and dialed digits were sent as audio tone signaling. In effect, IMTS was a trunked system, because any subscriber could use any free channel instead of waiting on one assigned channel. Standard trunking theory shows that a pool of channels shared this way carries more traffic at the same blocking level than the same channels used separately. That gain was real, but a pool of a few channels is still a small pool, and better efficiency could not make up for the shortage of channels.

IMTS operated in the VHF high band near 150 MHz and, in some areas, in the UHF band near 450 MHz. It kept the MTS architecture of a single high-power site per service area. A subscriber who drove out of that area lost service, and using the phone in another city generally meant going back through an operator under whatever arrangement the carriers had. IMTS service lasted in some rural areas well after cellular arrived, because a single tall site could cover thinly populated territory that early cellular systems had not yet reached.

A 1947 memo and a long wait for 800 MHz: the cell concept and its delay

The idea that replaced the single high-power site is older than most people expect. In December 1947, Douglas H. Ring of Bell Telephone Laboratories wrote an internal memorandum describing a mobile system built from many small coverage areas. Each area would have its own low-power site, and the same frequencies would be reused in areas far enough apart not to interfere. W. Rae Young of Bell Labs is usually credited alongside Ring with the hexagonal layout later used to draw cells. The concept attacked the reuse problem directly, since a channel confined to a small cell could be used again a few cells away instead of once per metropolitan area.

The memo did not produce a working service for more than thirty years. A cellular system needed more spectrum than the VHF and UHF mobile telephone allocations offered. It also needed a way to move a call from one cell site to the next as the vehicle drove. That required a switching office able to track every active call and command a mobile to change frequency in the middle of a conversation. The switching and control electronics to do this at reasonable cost arrived with computer-controlled telephone switching and, later, the microprocessor in the mobile unit.

The spectrum came out of the UHF television band. In the late 1960s, the FCC opened a proceeding on reallocating spectrum in the 800 MHz range to land mobile use. AT&T filed its proposal for a high-capacity cellular system in the early 1970s. The Commission’s allocation decisions stretched through the 1970s, and its 1981 order set the licensing framework. That framework provided two cellular systems in each market, each on 20 MHz, with one reserved for the local wireline telephone company and one for a non-wireline carrier. The same 800 MHz proceeding also opened spectrum to private land mobile users, including trunked systems, and many public safety trunked systems were later built there. For docket numbers and decision dates, go to the FCC’s own records of the 800 MHz land mobile proceeding rather than relying on summaries, this one included.

Telephone industry accounts often blame the gap between 1947 and 1983 on FCC delay, and the regulatory process was undeniably long. My reading is that both factors mattered. The spectrum dispute occupied most of the 1970s, while the control electronics that made handoff economical were still maturing in the same years. The record does not allow anyone to assign the delay cleanly to one cause or the other.

Chicago 1978 and October 1983: dating the trial, the launch and the myths

Several dates in this history get confused with each other, and the confusion usually produces a false first. The first is the AMPS developmental system around Chicago, which AT&T and Illinois Bell built to test the Advanced Mobile Phone Service design under real traffic. Most accounts describe equipment testing beginning in 1977 and service to paying trial customers beginning in 1978, with the customer count in the low thousands. I have seen the start of customer service given as different months of 1978, and I would not put a day on it without a primary source. The January 1979 issue of the Bell System Technical Journal was devoted to AMPS, and it is the best place to read the design as its engineers described it.

The second date is the commercial launch. Ameritech Mobile Communications opened commercial cellular service in Chicago on October 13, 1983. It was the cellular arm of the Midwestern holding company being formed ahead of the Bell System breakup, which took effect on January 1, 1984. October 13, 1983 is the date most US histories use for the start of commercial cellular service in the United States, and I am comfortable with it in that narrow form. A separate trial in the Washington and Baltimore area, run by a non-wireline company with Motorola equipment, came before commercial service in that market, which opened within months of Chicago.

A common myth holds that Chicago had the world’s first cellular network in 1983, and that claim is wrong. NTT opened a cellular service in Tokyo in 1979, and the Nordic Mobile Telephone system began commercial operation in 1981, so the defensible claim for Chicago is the first commercial cellular service in the United States. A second recurring error treats Martin Cooper’s call of April 3, 1973, made on a Motorola handheld prototype on a New York street, as the beginning of cellular service. That call demonstrated a portable unit a decade before any US commercial cellular system existed, and it is historically important on those terms. A third error describes the 1946 St. Louis service as early cellular, which it was not, since MTS had no cells, no frequency reuse and no handoff.

Reuse, handoff and a switch: what AMPS changed in engineering terms

AMPS kept analog FM voice on 30 kHz channels in the 800 MHz band, so the radio side of a conversation would have looked familiar to an IMTS engineer. The change lay in the architecture around it. A market was divided into cells, each served by a low-power site. Channels were assigned to cells in a repeating pattern, so a channel in use in one cell was reused in another cell far enough away to keep interference tolerable. Planners usually drew this as a grid of hexagons, and seven-cell reuse is the common textbook example.

Every cell site connected to a Mobile Telephone Switching Office, and the switch took over work that the IMTS base station and operator had never done. When a call was placed, the switch assigned a voice channel in the serving cell. While the call was up, it watched signal reports from the surrounding sites, so it could command the mobile to retune to a channel in the next cell as the vehicle crossed the boundary and move the call without dropping it. That process is handoff. Call setup ran on dedicated control channels carrying digital signaling, so the subscriber dialed as on a home phone, and the system handled channel assignment out of sight.

The capacity consequence made AMPS a real break with IMTS. In IMTS, capacity was fixed by the number of channels licensed in the area. In AMPS, capacity could grow by splitting busy cells into smaller ones and reusing the same channels more times across the market, at the cost of building more sites. The original allocation gave each of the two carriers in a market 333 channels, and each rose to 416 when the FCC added spectrum later in the decade. A large IMTS city, by comparison, might have had about a dozen channels.

The first AMPS subscriber units were mostly mounted in vehicles. Motorola’s DynaTAC 8000X handheld received FCC approval in 1983 and reached customers in 1984. Early cellular was expensive in both equipment and airtime, so, much like MTS, it spread through business users first. Its growth was limited by how quickly carriers could build sites and sell service rather than by a fixed number of channels in each city.

Radio as the link agencies controlled: how the mobile telephone years shaped doctrine

Throughout the MTS and IMTS period, an agency could put a telephone in a fire chief’s car or a police supervisor’s vehicle only if the carrier had room. Even then, the channels went busy at exactly the times a large incident would generate traffic. The service depended on a carrier’s operator, a carrier’s base station and a carrier’s decision about how many subscribers to admit, and the agency controlled none of them. Its own licensed radio channels, which public safety had been building since the late 1920s, were channels the agency could plan and repair itself. They also did something mobile telephone never did, which was to put one voice in front of every unit at once.

That experience shaped doctrine. In the communications SOPs I reviewed as a consultant, the common pattern assigns tactical and dispatch traffic to radio and treats telephones, cellular included, as administrative or supplemental. I think that reasoning owes a good deal to a generation of supervisors for whom a vehicle phone was a scarce and operator-dependent service. The one-to-many property matters as much as capacity. A fireground or a pursuit needs every unit to hear the same transmission, and a point-to-point phone call, however clear, delivers the information to one person.

Cellular solved the capacity problem under normal load. It kept the property that made MTS unreliable in emergencies, though: the agency shares a commercial network whose capacity is engineered for ordinary demand. When a disaster sends everyone to their phones at once, or takes out power and backhaul at cell sites, calls block much as they did on a dozen IMTS channels. The federal priority programs for wireline and wireless calls, along with FirstNet’s priority and preemption, exist because of that property. Other articles in this section cover Band 14, push-to-talk over cellular and the Katrina record, so I will leave the detail to them.

The balance has shifted since 1983 more than many SOPs admit. At many agencies, mobile data terminals, AVL, station alerting and push-to-talk over cellular now ride on commercial networks. The dependence on a carrier that early radio planners avoided has come back through the data side. The practical lesson I draw from the mobile telephone years is to know which functions depend on a carrier and what the radio fallback is for each one when that carrier’s network blocks or fails.

What to do at your agency

• This month, the radio system administrator should pull the trunking controller’s busy and queue report for last month’s busiest hour, and for the largest incident of the past year if those logs still exist, and bring a one-page summary to the next regular communications committee meeting.
• The communications director should write a one-page list of every operational function that currently rides on a commercial carrier, including MDT data, AVL, station alerting and any push-to-talk over cellular, and record beside each one the radio procedure crews use when that carrier is down.
• The emergency management director should obtain the current roster of agency phones enrolled in Wireless Priority Service and of personnel holding GETS cards from whoever administers them, and confirm that each person listed still holds the position that justified enrollment.
• The training officer should add a segment to the next scheduled multi-company drill in which crews run the scenario with cell phones and MDTs set aside, and record in the after-action report any task that stalled without them.
• The person who maintains the communications SOP should read its section on telephone use and, if it still calls cellular supplemental while dispatch data now depends on it, write one paragraph bringing that section into line with how the agency actually operates.
• Whoever maintains the agency’s training slides and website history page should check any claim of a mobile telephone or cellular first for the local city, and either attach a documented source or remove the claim.

Takeaways

• AT&T’s corporate history dates Bell System Mobile Telephone Service to June 17, 1946, in St. Louis, and that first is defensible only when stated narrowly, as Bell System commercial land mobile telephone service.
• MTS was half duplex, connected every call through an operator and could be heard by anyone on the channel, which made it much like renting a phone patch on a shared base station.
• Each MTS or IMTS channel carried one call across a whole metropolitan area, so capacity equaled the channel count, and carriers controlled blocking by keeping applicants on waiting lists.
• The widely repeated 1976 New York figure of about a dozen channels, 543 or 545 subscribers and about 3,700 people waiting appears in many histories in slightly different forms and should be cited as approximate.
• IMTS, introduced around 1964, added direct dialing, full duplex and automatic idle-channel selection, which made it a small trunked system without raising the channel ceiling.
• The cellular concept dates to a December 1947 Bell Labs memorandum by Douglas H. Ring, and the long gap before service reflects both an extended FCC proceeding over 800 MHz spectrum and the time needed for affordable switching and control electronics.
• Chicago’s AMPS developmental system served trial customers from 1978, and Ameritech’s October 13, 1983 launch was the first US commercial cellular service, while Tokyo in 1979 and the Nordic NMT system in 1981 came earlier.
• Agencies learned during the mobile telephone years to rely on radio they licensed and controlled, and the same question now applies to every function that rides on a commercial carrier.