H.324
H.324 is the international standard for multimedia communication over low bit-rate networks, including the PSTN and 3G mobile networks (H.324M, as it is called).
H.324 is an "umbrella" specification, which includes the standards H.324 and H.245. It allows for the use of T.120 for data collaboration and file transfer.
Resources: H.324 Information Site, VoIP Information Site