I just got a used Samsung Galaxy S Relay (Tmobile) phone used from someone. I'm trying to get it setup with Straight Talk. I got a SIM card from ST. Activated it. When I tried to make a call, I got the msg "Not Registered on Network." After several calls to ST, they decided it was a faulty SIM card so they sent me a new one. I activated that. Same problem. ST told me to contact Samsung. Samsung told me the phone probably needed unlocked. I bought an unlock code. However, I cannot seem to enter it. I inserted an active AT&T SIM card but it didn't ask for the code. Instead it worked and I was able to make phone calls out, no problem. However, the ST SIM still gives me a not registered on network error when I try to call. I have full service bars in my location as well. I've tried full factory reset several times and I have tried calling in several locations. Please help. This is getting really frustrating. Thanks.