Can I use my old 2wire gateway (model 2701hg-b) for my new ATT U-verse service? I used to have ATT high-speed DSL and recently switched to U-verse. They sent me a new Motorola "Modem" which I think is ADSL2+. The 2wire gateway is ADSL. My service speed is 1.5 Mbps.

I went over to DSL Reports, which is one of the oldest and best resources about broadband. This Thread looks like it has your answer. From what they say, your old modem shouldn't work. However, as part of upgrading to uverse, AT&T aparently will come out and replace old 2Wire vdsl modem with one that is uverse compatible.