SIP FAQ : SIP Functionality :
Does SIP support the standard telephone features?
- call forwarding unconditional, busy, ...
- call transfer (call control spec)
- caller ID
- call hold
- 3-way conferences and multiparty conferencing (call control spec)
- call return ("*69")
- call park (with NOTIFY)
- follow-me
- find-me
- call waiting
- IVR systems
- multiple line presences
- camp on
- call queueing
- automatic call distribution
- do not disturb
Some services, like repetitive dialing, station speed dialing, last number redial, and distinctive ringing, are implemented purely in the end system and require no support from the signaling protocol.
The Telecommunications Industry Association (TIA) is working on a recommendation http://www.tiaonline.org/standards/ip/ for business PBX-style services and other Internet phone requirements.
How does SIP provide message waiting services?