Simple Jailbreak question, please help?

I'm looking for help from anyone and everyone who knows anything about iPhones...

So I was given an iPhone 3GS and I currently have a phone plan with T-Mobile... I paid about 9 dollars on a website to allow me to jailbreak my iPhone 3GS.

To make a long story short, sometimes when I call "#06#" I'm able to get service. But about 90% of the time, I'm not able to make calls, receive calls, or text people/receive texts... I have no service


Does anyone know why this is? When I first jailbroke my phone, I was able to call people and text, now I can't do anything


Please help. Is there something I should upgrade or download?





EDIT: I just realized I meant to ask, how do I UNLOCK my iPhone 3GS and keep it unlocked? Not how to jailbreak it, whoops!