How do i use a tmobile sim card on my jailbroken iphone?

I have the first generation iPhone, and I've seen that its possible to run the iPhone with a t mobile sim card. How is this done? I have a t mobile sim card and I've downloaded the T-Mobile US Carrier(internet APN), but i still get the error from iTunes saying that the iPhone does not support that type of sim card. Please Help me!!

You need to unlock the iPhone. I suggest you can approach Mobileunlocksolutions.com and specify the country,locked network of iPhone.Based on the availability you can get the permanent unlock service along with free instructions.