Customers will be able to use portable computers for services such as video calling and IM as they move between Wi-Fi and cellular networks T-Mobile International will start offering a converged Wi-Fi and cellular service this summer, using network equipment from Nortel Networks, Nortel announced Friday at Cebit.T-Mobile customers will be able to use laptops and PDAs to use services such as video calling, video conferencing and IM even as they move between Wi-Fi and cellular networks. Their connections won’t be dropped as they move between the networks and the customer can use one phone number to be reached regardless of which network they are near, Nortel said.The companies are demonstrating the capability, which will work over 3G, EDGE (Enhanced Data Rates for GSM Evolution), GPRS (General Packet Radio Service) and Wi-Fi, at Cebit. The service will be geared toward business customers who will be able to use the service to access enterprise applications, T-Mobile said.Operators and vendors have been discussing such converged services recently but few have been commercially launched yet. BT Group has a service in the U.K. that allows users to roam from a cellular network onto a Wi-Fi network but it’s limited only to the user’s home Wi-Fi network.BT and others support a UMA (Unlicensed Mobile Access), a technology geared toward enabling mobile operators to offer converged services. T-Mobile’s system will be based on SIP (Session Initiation Protocol), an open standard that can also be used to deliver converged services. T-Mobile operates hotspots around the globe so this service could combine T-Mobile’s cellular and Wi-Fi networks. T-Mobile already offers customers the T-Mobile MDA Pro, a PDA (personal digital assistant) that includes both Wi-Fi and cellular. Technology IndustrySoftware DevelopmentSmall and Medium Business