"The Session Initiation Protocol (SIP) is a protocol developed by the IETF MMUSIC Working Group and proposed as a standard for initiating, modifying, and terminating an interactive user session that involves multimedia elements such as video, voice, instant messaging, online games, and virtual reality. In November 2000, SIP was accepted as a 3GPP signaling protocol and permanent element of the IMS architecture. It is one of the leading signaling protocols for Voice over IP, along with H.323."
MIT's VoIP infrastructure uses SIP as its standard signaling protocol. Technically this means that most devices that implement the SIP standard can theoretically be connected to MIT's VoIP infrastructure. What can actually be connected is of course limited by support, resource, configuration, and security constraints.