The subject is “Virtual Roaming for data services” and “Seamless Technology change” also called “Number Continuity”.“Virtual Roaming for voice and SMS” was covered in one of the author's previous book. “Virtual Roaming” means that it allows a subscriber to visit a network which his home network does not have an agreement with. The “Seamless Technology change” allows a user to keep all his services including reception of calls and SMS sent to his usual number when he switches his GSM to a Satellite phone or to WiFi. The implementation of Seamless Technology change uses...