Q: Unlock failing
I had my IPhone 3GS unlocked by contacting AT&T through website long time ago. Finally, I started to try it, yesterday. However, after finishing restore it is stuck on No Service even if there is no SIM card in it. iTunes says "There is no SIM card installed in the iPhone you are attempting to activate. Please disconnect and insert a SIM card in the iPhone". I don't have an original SIM and neither can I get another AT&T SIM but it is not saying me to insert correct SIM. There was working SIM from another operator when it was restoring. I tried to flash it in DFU mode without SIM and it was stuck in Searching... mode when it was powered on. Inserting SIM doesn't change it and iTunes again says me to insert one.
iPhone 3GS, iOS 6.1.6
Posted on May 11, 2016 12:22 AM
As far as I remember, you'll have to insert the SIM card that has been used when the phone was still locked, then change it to the new one during the setup process. Check this article:
How to unlock your iPhone for use with another carrier - Apple Support
Posted on May 11, 2016 1:03 AM