@Mark Ollig
The 1968 Carterfone decision was an important event in telephone history, but it is often mistakenly associated with President Jimmy Carter.
The 1968 Carterfone decision was an important event in telephone history, but it is often mistakenly associated with President Jimmy Carter.
It is actually named after Thomas F. Carter, an inventor from Texas, who invented a device which acoustically interfaces with a telephone called the Carterfone.
The FCC changed the AT&T Bell System’s phone company rules May 16, 1957, known as tariffs, in response to the 1956 Hush-A-Phone Corp. v. United States decision.
This decision allowed customers to use a small plastic Hush-A-Phone cup, invented by Harry C. Tuttle, to reduce noise and improve privacy on their telephones, provided it didn’t harm the network.
Following this case, the Bell System was required to permit such mechanical attachments.
However, AT&T’s rules still banned most other “foreign attachments,” especially electrical connections not provided by the company, including the Carterfone, from being used on the national telephone network.
In 1959, Thomas F. Carter invented the Carterfone, an acoustic coupler that allowed two-way radios to connect to the public telephone network without any electrical link to the Bell System.
The Carterfone’s base unit, about the size of a shoebox, connected by wire to a separate remote speaker used for monitoring and volume control.
A standard Bell telephone handset rested in the Carterfone cradle, its receiver and transmitter seated in paired rubber cups.
Inside the base were a small microphone, audio circuitry, and a voice-activated switch.
The FCC opinion later described this as a “voice control circuit” that keyed the radio transmitter when the telephone caller spoke.
In a typical setup, the mobile vehicle carried a standard two-way radio, and the base office had the matching base-station radio, a Bell telephone on a POTS line, and the Carterfone.
When a driver needed to reach someone on the telephone network, they first called the dispatcher over the mobile radio.
The dispatcher answered on the base-station radio, lifted the telephone handset, and placed it into the Carterfone’s rubber cups, and dialed the destination number.
On the telephone side, the caller’s voice traveled over the copper POTS line to the handset.
Sound from the handset’s receiver entered the Carterfone’s rubber cup, where the microphone and voice-activated circuit detected it and keyed the base-station radio transmitter.
This sent the audio out over the two-way radio channel to the driver.
The return audio followed the opposite path.
When the driver spoke into the vehicle’s radio microphone, the mobile radio carried the sound back to the base-station radio, which fed it through a cable to the Carterfone’s separate speaker.
That speaker directed the sound into the rubber cup at the telephone mouthpiece, allowing the distant party on the POTS line to hear the driver’s voice, still without any direct electrical connection to the Bell System.
The Carterfone used electrical connections only on the radio side, while the telephone side operated purely through sound.
This acoustical arrangement enabled two-way radios to be linked to the public telephone network without touching the Bell System’s wiring.
AT&T would not allow the Carterfone to connect to its network, calling it a foreign attachment under its rule that allowed the company to cut off service to any device not supplied by them.
As a result, AT&T could disconnect customers who used the Carterfone, even when it was providing vital service in remote areas.
Facing restrictions that threatened his business, Thomas F. Carter and Carter Electronics Corporation sued AT&T Nov. 29, 1965, in the US District Court for the Northern District of Texas.
Carter argued in his antitrust suit that AT&T used its tariffs to control which devices could connect to the network.
The federal court then referred the tariff issue to the FCC for review.
In August 1966, the Fifth Circuit upheld that referral, and the FCC proceeded with a formal investigation.
Carter filed a complaint under the Communications Act Dec. 21, 1966, claiming the tariff restricted trade.
During hearings in 1967, AT&T said its tariff rule was needed for safety, but Carter and others argued it was anti-competitive.
The FCC determined June 26, 1968, that AT&T’s tariffs were unlawful, allowing customers to connect their own devices provided they did not harm the network.
The Minneapolis Tribune reported June 28, 1968, that the FCC voted six to zero to overturn the rule allowing phone companies to block customer attachments.
The ruling ended AT&T’s de facto equipment monopoly and opened the door to competition in the sale of telephones, modems, answering machines, and business telecommunication systems.
A Minneapolis Tribune story on March 11, 1969, reported that Data Communications Systems, Inc., of Columbia Heights had completed its acquisition of Carterfone Communications Corporation of Dallas, TX.
The Carterfone decision pushed back against AT&T’s control over customer equipment.
In response, the company updated its tariffs to require any customer-owned devices to connect through a Bell-owned Protective Connecting Arrangement (PCA) box.
This was a physical interface installed by the Bell Telephone Company between their wiring and the customer’s equipment, with every device wired through it.
Similar to the later network interface device (NID), the PCA marked the handoff point between customer and company, but unlike the NID, which gave customers direct access to their inside wiring, the PCA kept that wiring entirely under Bell’s control.
Because it sat at the handoff point and was off-limits to customers, it restricted their access to their own wiring and limited many of the benefits promised by the Carterfone ruling.
In 1975, the FCC established Part 68 rules in Title 47 of the Code of Federal Regulations for connecting customer-owned equipment to the telephone network.
These rules helped pave the way for the NID, which telephone companies increasingly installed on the outside of buildings after the 1984 breakup of the Bell System, as the handoff demarcation point between their wiring and the customer’s wiring.
These rules replaced the PCA requirement and defined “harm” as hazards to staff, damage to network equipment, billing issues, or degraded service.
The FCC set national standards and introduced a registration program, enabling phone companies to block harmful devices.
This change enabled connecting non-Bell devices, such as consumer telephones, answering machines, modems, and business phone systems, via standardized modular connectors known as registered jack (RJ) connectors.
Among these, RJ11 emerged as the standard modular jack used with single-line telephones.
Part 68 promoted a competitive market by allowing consumers to purchase phones and other equipment from various manufacturers, effectively ending the equipment monopoly held by AT&T and its manufacturing division, Western Electric.
Thomas F. Carter passed away Feb. 23, 1991, at 67.
Today, a Carterfone is on display at the Smithsonian’s National Museum of American History as part of its telecommunications collection.
