Do you get an error when you insert the sim? If so then the phone needs to be unlocked. One of the unlocking vendors here may be able to help you: Cell Phone Market - Cell Phone Forums

I have my Tracfone SIM in the new phone I got. I didn't notice it was a Net10 phone until after I got it. Three Tracfone people assured me I could transfer it back to Tracfone. Now they are saying I can't. I wanted my huge number of Tracfone minutes and double minutes contract. I would have sent the new phone back if I had known soon enough. Where is the phone locking anyway - on the SIM card or elsewhere? Thanks.