Much better than iSip... Recommend - not perfect, but better than others

Performance on this app far exceeded that of its competition iSip. User interface could use a little more work, but no doubt on future releases it will improve.
The heart of the issue is performance. After having issues with another softphone, this one works well with an Asterisk PBX, and my callers report that it sounds much better. If youre looking for a SIP client to use with Asterisk or Trixbox, I would recommed you try this app

B767Driver about WeePhone SIP