Since I got it, I have used it off and on, always behind the router, and in addition to PAP2T.
I had to reset it from back button originally since it would not connect, once done, and populating provisioning field, it provisioned and connected right away, not a single hiccup so far.
When I power it up, shows up in vpanel. Phone connected to it rings with PAP2T connected phones, and essentially works like a cloned line.
I have setup distinctive rings for some of my phone numbers in vpanel, and it works great on both PAP2T and rt31P2.
My router is MONOWALL.

dvijen