The ITU-T video conferencing scheme protocol (H.323) is a Video Conferencing protocol, which allows video and voice calls to be made over the Internet. H.323 calls originally required the use of a specially equipped TeleConference studio, but low quality calls are now able to be made from a Personal Computer. Just copy & paste the full IP address into your H.323 SoftPhone (the URI to precede the address is "h323:"). Below are addresses to various free public access H.323 servers.
[IANA Port assignment = 2517]

H.323 Servers