This is affecting BB data access. After over a month of troubleshooting and denial by both RIM and T-Mobile, I finally got a tech support rep to admit that there is an issue affecting only 646 numbers on the data network end. They have service tickets on the problem but given that this has been going on for so long I'm thinking it has to do with the upgrades to 3G going on, since they worked so hard to deny this problem for over a month.

Hmm - we have lots and lots of 646 numbers. No complaints. Is this locally (one tower) or all over?

There are 3 or 4 instances of it in Queens NY that I know of personally, so it could be just there. But they did say there were a few towers out in Manhattan which is causing this. And it's ONLY for BB data, regular web is fine (correction).