I just switched to Cingular / ATT from T-Mobile 3 months ago. When I first switched, I signed up with unlimited media max bundle and had issues connecting. I was told I had to switch to one of the PDA connect plans for it all to work correctly. As soon as I did, I was able to connect with no problems. The network may be preventing you from connecting because you don't have the correct plan. It's just another way for them to get more money out of you.