SIP library for iOS with non-GPL license
These are the ones I know about:
Proprietary:
- vaxvoip
Open source: GPL/LGPL
- sofia-sip
- linphone
- exosip
oSIP is LGPL and therefore can be used (as a library) in commercial and closed-source projects. It compiles easily for arm. It is the SIP library used by linphone for iPhone; however, linphone is GPL.