trade AT&T gateway modem for Comcast gateway modem

My promotional year ran out, so I am switching from AT&T to Comcast sometime between now and 6/21/2014. Right now AT&T is offering $15/mo for 6Mbps "Uverse" for 1 year, so if you are on Comcast (or looking for a new internet provider), perhaps you are switching to AT&T.

I am offering an AT&T modem+router (2WIRE 3600 HGV) in exchange for a Comcast Xfinity-compatible modem+router (http://mydeviceinfo.comcast.net/). I'm also willing to sell the AT&T gateway modem (used 1 year) for $50.

Please check that it is the right one for your AT&T connection - the networks are different at different addresses.