In addition to the PAP2 from VOIPo, I have another PAP2 from NextAlarm, and a couple of old Azacall/UTStarcom adapters from Lingo that I use for fooling around with other services (Google Voice, SipSorcery, Callcentric, IPKall, etc.). Some of these setups require that I be able to reach the adapter directly from another adapter -- i.e., without a SIP proxy in between. These direct connections could not be made without port forwarding, since an external caller needs to be directed to the appropriate device. However, several people have reported using multiple adapters without any port forwarding at all, with no problems. YMMV.