"Authentication" is a new system AMPS cellular carriers are using to combat fraud. Motorola claims it was the first to implement it in its phone, starting in 8/95. Other phones authentication-capable include the Nokia 100, 232 and 638 models, and Audiovox's 460, 560, and 850A. Bell Atlantic-Nynex Mobile (BANM) was the first carrier to use this system, installing systems in New York City and northern New Jersey in May of 1996. Since that start, Washington DC, Baltimore, Philadelphia and recently Boston/Providence BANM systems have implemented authentication. BANM plans to have it's entire system converted by the end of 1996.
AT&T Wireless started using authentication in New York City and South Florida, also in May of 1996. They also claim to be the first to use it. AT&T will have authentication fully deployed by the end of 1996.
VodaFone in the U.K. has an authentication system, I do not know how similar it is to the one in use here in the U.S. VodaFone's authentication sends an additional parameter along with the ESN, calculated from the ESN and the Dialed Number. Somehow, a PIN is added.
Models supporting A-key authentication: