X-PRO for MAC OS X   
by CounterPath Solutions, Inc.   

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
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
.. and much more!