Tmobile sim card can't be recognized in iPhone?

I jailbroke and unlocked my iPhone 3GS locked to AT&T, but I'm wanting it to work with tmobile. I put the sim card in but it doesn't get service still. The sim card has a data plan and everything. The sim card is at least 6 years old. Do I need a new one? Or how do I make the tmobile sim care work? I used redsn0w to jailbreak it.

You can use http://www.iPhoneAdmin.com to check if its really unlocked