The Carterfone is a device invented by Thomas Carter. It manually connects a two-way mobile radio system to the public switched telephone network (PSTN), making it a direct predecessor to today's autopatch.
The device was acoustically, but not electrically, connected to the public switched telephone network. It was electrically connected to the base station of the mobile radio system, and got its power from the base station. All electrical parts were encased in bakelite, an early plastic. When someone on a two-way radio wished to speak to someone on phone, or "landline" (e.g., "Central dispatch, patch me through to McGarrett"), the station operator at the base would dial the telephone number. When callers on the radio and on the telephone are both in contact with the base station operator, the handset of the operator's telephone is placed on a cradle built into the Carterfone device. A voice-operated switch in the Carterfone automatically switches on the radio transmitter when the telephone caller is speaking; when he stops speaking, the radio returns to a receiving condition. A separate speaker is attached to the Carterfone to allow the base station operator to monitor the conversation, adjust the voice volume, and hang up his telephone when the conversation has ended.
Landmark regulatory decision
This particular device was involved in a landmark United States regulatory decision related to telecommunications. In 1968, the Federal Communications Commission allowed the Carterfone and other devices to be connected directly to the AT&T network, as long as they did not cause harm to the system. This ruling (13 F.C.C.2d 420) created the possibility of selling devices that could connect to the phone system using a protective coupler, and opened the market to customer-owned equipment. The decision is often referred-to as "any lawful device", allowing later innovations like answering machines, fax machines, and modems (which initially used the same type of manual acoustic coupler as the Carterfone) to proliferate.
In February 2007, a petition for rulemaking was filed with the FCC by Skype, requesting the FCC to apply the Carterfone regulations to the wireless industry — which would mean that OEMs, portals and others will be able to offer wireless devices and services without the cellular operators needing to approve the handsets. However, on 1 April 2008 FCC chairman Kevin Martin indicated that he would oppose Skype's request. 
- Hush-a-Phone v. United States
- Cordless telephone
- Terminal equipment
- Citizens' band radio
- McCullagh D (2008-11-07) Democratic win could herald wireless Net neutrality. CNET, viewed 2010-06-01.
- Full text of FCC Carterfone decision
- Full text of Skype petition
- Cybertelecom :: Customer Premises Equipment - FCC Regulations concerning attachment and marketing of CPE
- Timeline from NPR
- ArsTechnica: Any lawful device - 40 years after the Carterfone decision (includes picture of the Carterfone)
- Carterfone: My Story, by Nicholas Johnson, FCC Commissioner, 1966-73