Samsung

First, thank you for your response. When you say the phone Samsung sgh-i937 will not connect using straight talk unless i got the phone unlocked through at&t? So if I walk in the store they will do that free or charge for that unlock or is that something I have to figure out using the internet. Also, I wonder who I would ask other then straight talk about the sim since they are in the business of making money I would hope at&t might know if the sim is ok or where it is straight talk they may turn there nose up? Thank you!