I moved from T-mobile to AT&T. After that I tried to copy phone#s from my old phone to new phone by first copying them to SIM (t-mobile) on the old phone. Then inserting the SIM(t-mobile) in my new phone (at&t). That didn't work as it said unrecognized SIM. So I tried other way around. I inserted my new SIM (at&t) to my old phone(t-mobile). When I started the phone(t-mobile), it told me to enter "subsidy password". WHAT DO I DO NEXT?
OK, there's a couple of things going on here. First off, your T-Mobile SIM is no longer active, which is why it says "unrecognized SIM". You should still be able to move the contacts to your new AT&T phone. That is "IF" your AT&T phone is unlocked (or you'll run into another subsidy password request). Your old T-Mobile phone IS locked, which is why your AT&T SIM causes the password message to come up. Unlocking phones is a whole other issue, but this would explain why you're running into these issues.