Transferred Account Procedures (TAP) is a collection of procedures used in GSM to send billing records of roaming subscribers from the visited mobile network (VPMN) to their respective home network operator (HPMN).
TAP is essential for GSM roaming, because it allows a mobile subscriber to use his or her own mobile phone when visiting another mobile network.
There are different versions of TAP. TAP evolved from TAP1 through TAP2 and TAP2+ to TAP3. The latest release, TAP3, includes support for inter-standard roaming in a satellite network, WLAN and UMTS and other 3G technologies.