I have a Galaxy S7 that was purchased with Straight Talk. Recently, I tried to switch to Cricket wireless. The number was ported, the service was activated, but the phone still behaved as if it was locked. Long story short, we found out the phone is CDMA, but also has a sim card slot. I don't know much about this stuff, but I thought only GSM phones had removable sim cards. When you look in the settings under Mobile Networks, the only options are "LTE/CDMA" or "CDMA". Is this phone both GSM and CDMA compatible, and needs flashed or something? If so, how would I do that to work with Cricket, which is AT&T? Forgive me if these are stupid questions. I plead total ignorance.