Generic Access Network or GAN is a telecommunication system that extends mobile voice, data and multimedia (IMS/SIP) applications over IP networks. Unlicensed Mobile Access or UMA, is the commercial name used by mobile carriers for external IP access into their core networks. More recently, the system has been called Wi-Fi Calling by a number of handset manufacturers, including Apple and Samsung, a move that is being mirrored by carriers like T-Mobile US.