a method and system to provide gsm subscribers roaming into cdma or tdma networks , and cdma or tdma subscribers roaming into gsm networks , with basic call delivery wireless services as long as the roamers can pay the bill with their valid credit card , and to do so independently of and as a bypass of gsm memorandum of understandings for cellular / pcs services . this is achieved by integrating the proper pieces of wireless and wireline networks and secure communications , using ip networks and protocols as an alternative to the existing telephony - based approach .