GSM and CDMA2000
AMPS and D-AMPS have now been phased out in favor of either CDMA2000 or GSM which allow for higher capacity data transfers for services such as WAP, Multimedia Messaging System (MMS), and wireless Internet access. There are some phones capable of supporting AMPS, D-AMPS and GSM all in one phone (using the GAIT standard).
Read more about this topic: Advanced Mobile Phone System