GSM Shield SIM card troubles

So I'm trying to use the GSM shield to communicate with my smart phone. The SIM card that came with the shield only works with other devices on that network, and it's an obscure latin network that I don't have so I cant use that one, and I bought another t-mobile SIM card activation kit, but I can't figure out how to activate it without having an actual T-mobile number. Somebody please help me! Either help me figure out a way to get the T-mobile SIM card to work or tell me what other SIM to use! Time is kind of important aswell, as I am working on this project for an independent study at school, and I'm about to start getting bad grades because of this problem. Thank you!

Why don’t you ask the place where you bought the SIM card?

Assuming you've bought a Pay-As-You-Go card, don't you know anyone on the network who can register it for you? Otherwise get a sim card for a network where you can register it.