X-PRO for Mac

From Xten Networks:

premium SIP-based User Agent with all the features and functionality of a small business phone system. Open standards-based design allows for maximum network interoperation and integration. VoIP networks are expanding at a blistering pace, X-PRO is ready.
Conferencing plays a big part in any business. Take advantage of X-PRO tele-conferencing capabilities and combine up to seven PSTN & IP connections simultaneously. The Quality of Service will amaze you and the ease of use will prove it's worth. Let it run on a dedicated PC, turn-on Auto-Conference and it becomes a private conference server. Invite users to dial-in from their land-line legacy telephones, cellular phones or even connect from their PCs and PocktPC devices, all at the same time and you pay nothing more than the cost of your Internet connection.
Multiple-Network Support allows interoperation between several PSTN and IP SIP networks simultaneously. Already a powerful untility, when combined with X-PRO Conferencing this tool is truly awesome.
X-PRO Features: -Touch-tones [DTMF] -6 Lines -Line Hold -Line Transfer -Do Not Disturb -Inbound Call 'Ignore' -Inbound Call 'Go to Voicemail' -Call Forwarding URI/URL -Voicemail URL -10 Party Conferencing [IP & PSTN] -Auto-conference -Multiple SIP Proxy Registration [10 Proxies] -Dial/ Redial/Hangup -Auto-answer -Dynamic CODEC Selection -Caller ID [SIP ID] -Call Timer -Silence Threshold -Backspace/Clear/Delete -Mute -Microphone & Speakers Levels -Microphone & Speakers Meters -Push-to-Talk -Last Caller-ID -Recent Calls Dialed -Recent Calls Received -Sound Device Selection -Direct IP to IP Calling -New Familiar-looking Menu -Phonebook [Import/Export CSV] -Speed Dial