I'm not to familiar with how the 2wire AT&T DSL home network is setup. But if its anything like any other normal home network setup then it could be issues with your NAT type:
Type 1 - Connected directly to the internet (no router/firewall). Should have no issues.
Type 2 - Connected through a router properly. Should have no issues.
Type 3 - Connected through a router without open ports or DMZ setup for PS3. Everything should function properly, but you may have connection, voice chat or other issues.
An overkill, simple way to fix it would be to give your PS3 a static IP addres and put it in a DMZ on your wireless router/modem. This makes your PS3 completely unprotected by your router and can create some serious security problems if your not careful.
You can also open up the ports on your router. TCP: 80, 443, 5223 UDP: 5223, 3478, 3479, 3658
More info and general directions here
Another thing to look into would be weird UPnP connection collisions. I saw similar network drops after a certain period of time online when running a media server on the same network.
More info and people with wireless network drops here