I purchased my 6s full price from Apple as the T-Mobile model. When I received my device, I immediately took out the T-Mobile SIM before powering it on and I put in my AT&T SIM to complete the activation. I was wondering if that somehow botched the unlock status of my phone? One day I tried putting a T-Mobile SIM in my phone, and my phone threw the "No SIM" message. I also don't have the "Carrier" option in my settings menu. Any advice guys?