I had no bad or good opinion about pjsip library since i havent tried it yet

Better do some enquiry about the library to someone who had used it, and then decide whether you will be using it or not... And, i'm not at all a fan of Opensource..

And, documentation of almost all opensource libraries i'd seen concentrating on SIP sucks plainly like all other most opensource projects... so better try a library from a site who provides a fair documentation and a support forum... else, things might lead into horror..