Acrobits GroundWire is a full-featured SIP client which supports all the features of the business phone. It's the most feature-rich SIP client running on iPhone, iPad or iPod Touch.
Acrobits’ new business client has all the features of Acrobits Softphone, as well as these great new additions:
•Multitasking background support for iOS4
•Transfer and attended transfer
•Multi line
•Call Grouping
•Conference calling
•Customizable ringtones
•HD Wideband audio through G.722
•Completely redesigned audio optimized for the best VoIP experience on the iPhone
•Number rewriting, enabling you to utilize your existing contacts without having to create new entries to satisfy the dialing requirements of your PBX or SIP provider
•Address Book Matching to automatically format your contacts into the proper international format
Supported codecs: G.711 alaw, G.711 ulaw, GSM, iLBC, G.722 wideband (all included and ready to use) and also G.729 (available as an in-app purchase from within the app)