BlackBerry Curve 8320

When I first purchased my blackberry curve, I did not sign up for the data plan. At that point, MMS messages came in, and sent out fine. Once I added the data plan, I now get a message saying i have a new MMS message, but it could not retrieve the content at that time. I am given the option of manually retrying, most of the time, this does not work, and never works for messages sent from non-BB devices.
I have been on the phone with Tmo tech support BB division, which has not helped.
We have already tried things from hard power cycling to removing services in my service book, and repopulating over the network.
Has anyone else had this problem, and how did you fix it?

Thanks