said by todd54:
Can I look at the outside box to confirm which twisted pairs are used?
Absolutely. Head out to the Telco box (aka NID) on the side of your house, typically by your power meter, with a flat head screwdriver. There should be a screw marked "customer access" -- loosen that, then open the door, and see what wires connect to the AT&T service entrance module.
If I had to guess, the wire pair is green/green-white. That is the de facto standard U-Verse techs use for the VDSL2/ADSL2+ (depending on flavor) data feed to the modem
If you need assistance identifying what is what @ the NID, feel free to take a photo & post it. And officially, leave the screws labeled "Telco Access Only" alone...
A little more information on NIDs: »AT&T Southeast Forum FAQ
»NID (Network Interface Device)?