The Kev Master tried doing this with his AT&T sim and it looked ok.
Today, he got the free T-Mobile SIM and put it in and found that it wasn't unlocked so he tried doing this again and easily unlocked it.
The Kev Master
President of The 4th Persons Underground Society
The People's Champion on Twitter @thekevmaster
The Selma Syndrome - Posting a deal without full disclosure.