All field mappings have been cleared and I have an unlimited data plan. I have set up the blackberry internet service on t-mobile's site and that part works (I get mails through the blackberry service), when I try to perform enterprise activation, it fails.

Nokia E-90 with latest firmware (300.x), BBC 4.0 (from nokia for business site) and my company runs BES 4.1.6

EDIT: Just confirmed that it was able to activate, but fails to send/receive mail on the account.

Do you have the BlackBerry Internet Plan or the BlackBerry Enterprise Plan?

I have: "BlackBerry Unlimited Web + 400 Messages"

Does this make sense?

EDIT: do I need the following one instead?

"BlackBerry Unlimited w/Enterprise E-mail Add-on "

I don't know too much about BBC, but to connect to the BES you will need to be provisioned through your carrier for enterprise access.

I think you just have an unlimited data plan and for BES to work- it needs more than just unlimited data, they need to provision your SIM card with BES and for some carriers (like ours here in the Phils) it entails additional charges. It enables your SIM to use BES and not just data (GPRS/EDGE/3G)

I think the "BlackBerry Unlimited w/Enterprise E-mail Add-on " you mentioned is worth an inquiry- this might be the BES plan for your carrier..

Thanks !