IP Multimedia Subsystem (IMS) is an integrated network for telecommunications carriers that uses the IP protocol as its foundation for packetized voice, video and data. Supporting voice over IP (VoIP) in all its flavors (SIP, H.323, MGCP, etc.), the IP Multimedia Subsystem (IMS) is designed to interface with the PSTN and provide traditional telephony services such as 800 numbers, caller ID and local number portability.