If you look in the Linksys pages, you will find that they only offer two devices which combine NAT routing and SIP telephony, for domestic use:
2) RT41P2-AT: This is a much more capable device, combining the NAT abilities of a Linksys product with the SIP abilities of a Sipura. Looks like it should fill my needs. EXCEPT that this product only works in conjunction with the AT&T CallVantage service.
So, it looks like the folks at Sipura/Linksys/Cisco believe that if you want to experience IP telephony from your home, you have to sign with AT&T.
Isn't there a RT41P2-NA??
-Ramon F Herrera
Technical note: I have assembled a SIP network with about a dozen ATAs in 4 countries, and have seen all kinds of NATs, etc.