iPhone 3G "Could Not Activate Cellular Data Network..."

I have the iPhone 3G but I have recently updated to the new 3GS software. Everything is working fine, and when I am in a strong area, WiFi also is working fine. However, if I try to connect to the internet or use any applications that involve the internect (i.e. Facebook), an error message comes up that reads:

Could Not Activate Cellular Data Network: You are not subscribed to a cellular data service


So, I went into the apple store and explained the entire situation. Before that, I called my service provider and went through lots of trouble shooting and double checked that my plan was correct. Everything was fine from that standpoint so the next step was Apple. I went in and they checked to make sure that nothing was wrong with my Sim Card. It was fine. Then, they restored (or something not sure, they took my phone in the back for a few minutes and i believe restored it). Essentially, I had my phone replaced to another iPhone 3G. EVERYTHING WORKED. Then I went home and installed the new S software again. Now, the same situation with the internet begins.

I realize the obvious pattern that this problem is somehow related to the installation of the new software.

Help or any comments would be appreciated.
Thanks 🙂