Take it easy folks...The guy is just asking a question. I didn't have a credit card when I was 19. Anyway....
It sounds like you may have 1 or 2 problems. Is the BB asking you for a password to get into the BB? If not, then the Enterprise Activation "code" you are referring to, is that the icon on the home screen that asks for an email and a password? You don't need to use that. You can just hide the icon or leave it and don't use it.
As for the sim card problem, if the phone is "sim locked" (different than the phone being locked and requiring a password to get in) then you will need to have your friend call TMobile and see if he can get an unlock code from TMobile. The only way TMo will give an unlock code is if you are a customer in good standing (meaning you pay your bill on time.) If he can't get an unlock code from TMo then you'll need to pay one of the 3rd party unlocking services to get you an unlock code. There's no other way. Reputable unlocking services are GSMPhoneSource.com and some others listed in our sponsors forum.
If you don't have a credit card, try to find someone who does and just pay them back, if possible.
If/when you get it unlocked the BB could still have IT policy restrictions on it. You may have to remove that. See this link
for information on how to do that.
I know it seems like a pain, and it is. It's just the way the cell phone/BB world works.
Hope this helps.