ANSI-41 (IS-41) is a standard for identifying and authenticating users, and routing calls on mobile phone networks. The standard also defines how users are identified and calls are routed when roaming across different networks.
ANSI-41 is the standard used by AMPS (analog), IS-136 (TDMA) and CDMA networks.
GSM and WCDMA networks use a different standard, known as MAP.