GAN (3GPP standard) is another term for Generic Access Network and WAN is Wide Area Network. GAN is simply UMA or Wi-Fi.
Originally Posted by canguler87
The most common application of GAN is in a dual-mode handset service where subscribers can seamlessly roam and handover between wireless LANs and wide area networks using a GSM/Wi-Fi dual-mode mobile phone.
WANs are used to connect LANs and other types of networks together, so that users and computers in one location can communicate with users and computers in other locations.
Current 3GPP standards incorporate the latest revision of the GSM standards. 3GPP's plans for the future beyond Release 7 are in the development under the title Long Term Evolution.