Follow up: I added a Panasonic SIP corded/cordless combo behind the router, right along and in the same
subnet, no port forwarding. This is using Uverse RG. BTW, the only way to "replace" the router with Uverse is to place a router in DMZ hooked to their RG device, as it contains the vdsl modem component. Anyway, happy to report all appears to work well. Still have plans to add a static ip maybe...will see if any issues crop up.

I can also say the Panasonic KX-TGP550 and 551 work quite well. Have it registered with VOIPo and CallCentric too.