So far, Siphon is the best SIP app I've tried. MobileVOIP and TruPhone are very nice too (and don't need jailbreaking). Other apps offer at least some SIP features such as Nimbuzz, Fring, Viber and ...
Is it possible to unmask the SIP credentials stored in the Preferences of the Zoiper VoIP application ? I couldn't find any password unmask application for that and I can't find the password in my ...