After reading this article on your
http://www.networkworld.com/article/2186819/lan-wan/motorola-s-nvg510-dsl-modem----not-very-good.html modem, I can understand the wanting to replace it.
Slow Pri wrote
I would do a modem such as the Linksys CM3008:
that is a COMCAST CAble modem, he has ADSL. that will not work for him
are just an AT&T ADSL customer or a U-verse Customer ? thers is a difference between the internet systems
"Customers with AT&T uVerse will still need to purchase a modem directly from AT&T as using your own modem isn't allowed at this point. " well I guess that is that....
I did find this one on AT&T web site fod ADSL service : Netgear Model 7550
https://www.att.com/accessories/specialty-items/netgear-dsl-gateway-model-7550.html#sku=sku8150393