I'm just gonna throw this out there.... I have 3 devices on my network that require registration. My Voipo PAP2T, my PAP2, and my Grandstream IP phone. I checked my PAP2T against my PAP2 line for line and there is only 1 difference, my PAP2 has a stun server and my PAP2T does not. My PAP2 has never lost registration, while my PAP2T has lost it many times over the last few weeks.

My IP phone also uses a stun server, and has also never lost registration. Could there be something to this ?