IETF
ITSP
ITU-T

IETF (Internet Engineering Task Force)
The Internet Engineering Task Force (IETF) is charged with developing and promoting Internet standards. It is an open, all-volunteer organization, with no formal membership nor membership requirements

ITSP (Internet Telephony Service Provider)
Internet Telephony Service Provider. An ITSP's business model is primarily based on usage revenue generated through voice traffic carried over an IP network.

ITU-T ( International Telecom Union telephony )
(Befor called CCIT-T) The ITU Telecommunication Standardization Sector (ITU-T) coordinates standards for telecommunications on behalf of the International Telecommunication Union (ITU)