A wireless communication system for supporting multimedia services (MMS) provided to a user of a wireless transmit/receive unit (WTRU) which communicates with the wireless communication system. The wireless communication system includes a third generation partnership program (3GPP) universal mobile telecommunications system (UMTS), a wireless local area network (WLAN) and an MMS server. The MMS server stores at least one MMS message for the WTRU in a memory until the WTRU retrieves the message. The 3GPP UMTS includes an internet protocol short message gateway (IP-SM-GW) having a short message service (SMS) proxy. The WTRU is registered with the SMS proxy to establish SMS connectivity, and is also registered with the MMS server to establish MMS connectivity. The WTRU is notified when the MMS server receives an MMS message for the WTRU. The WTRU then retrieves the MMS message from the memory of the MMS server.