dbmaven, Here are few trouble shooting steps..

* Update latest firmware ( you probably already did this). Sometimes going back one rev will fix things too.

* Try turning off STUN on PAP2T and disable SPI on router. No port forwarding. See if it works. When you are doing these steps, keep the registation interval to 1 minute, so that the registration expires quickly. Also wait for 1 minute before you goto the next step.

* If it doesn't work, turn on STUN in PAP2T, disable SPI on router, See if it works. There are lot of parameters for STUN in PAP2T. You might have to change things few times.

* Try port forwarding. 5061 and 5062 are PAP2T defaults. I am not sure if they changed one of those to 5079 for you. 5079 was used by GS 502. Since you had problems with registration, I think just forwarding those ports will check if the registration will stick.

* See this thread (see sipmaster posting) http://forums.linksysbycisco.com/lin...=99574#M126691

He seems to say 610N modifies SIP packets and maybe doing it incorrectly.

http://forums.linksysbycisco.com/lin...id=99574#M3724

* If you are able to get it to work, then you can add SPI firewall and see if it breaks things.

* To sniff the packets, you need wireshark and a hub. Put the pap2t and pc behind the hub. Connect the hub to the router. Use Wireshark to capture the packets.