What are the steps in unlocking a G3 cellphone from Japan to use in the USA? -

I recently bought a 903t Vodafone cellphone from Japan. I know that I can use T-Mobile in the States with this phone. I used someone else s SIM Card and inserted it into the phone and got a message saying that this SIM card cannot be used. What steps should I be take at this point to get this phone to work? Should I just take it to t-mobile and have them insert one of their SIM cards,etc?

2 ways 1.go your carrier and they unlock it to be used worldwide 2.goto some cell phone repair shop and they do the job with the software and cables and stuff.