Patent ID: 7301934

Claim:
A Universal Mobile Telecommunications System (UMTS) telecommunication system including a mobile station, having a Mobile Subscriber Integrated Services Digital Network (MSISDN) number associated with the station or its user, and means for enabling the mobile station to receive Voice-Over Internet Protocol (VoIP) calls established when dynamic Internet Protocol (IP) addressing is used and the mobile station is not in an active Packet Data Protocol (PDP) context whilst roaming away from a home network, comprising: means for informing a serving Gateway GPRS Serving Node (GGSN) of the roaming network of the International Mobile subscriber Identity (IMSI) of the called mobile station, and means for enabling a serving VoIP call control server to map a called MSISDN number to the IMSI number, and further including an interface between the serving GGSN and the serving VoIP call control server, enabling the GGSN to receive a request from the VoIP server to initiate PDP context set up procedures using the IMSI number of the mobile station.