At this point, I am going to have to say PJSIP is not ready for primetime. I've been trying to use it but just run into too many roadblocks. Cisco 79xx series (old) phones will not register, Grandstream phones I have tried will not register and trunk connections to Vitelity will not connect. The only bright spot I have found is that Yealink phones will register.
All of it works with CHANSIP. YMMV.