A.K.A. A-key

"Authentication" is a new system AMPS cellular carriers are
to combat fraud. Motorola claims it was  the first to implement it in its
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&ampT 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: