After trying far too many SIP clients I installed SessionTalk. It is the only SIP client so far that has remained both usable AND stable for multitasking iOS. All others, for more money and theoretically more features just keep freezing or crashing, but SessionTalk keeps chugging along.
And all fanciness aside – I need the phone/sip to work first, get fancy second. If we can get g.729 that would be my *only* additional request.
Good stuff guys!
Cornelius Talmidge about SessionTalk Pro Softphone, v2.3