I recently smashed my old device in my car trunk and needed to find a replacement. I was on AT&T running a OnePlus 8. A friend just bought a Galaxy S21 and had his old Verizon LG G7, stock, sitting around so he sold it to me for $60. I thought I had seen somewhere that it would work so I threw my SIM card in. Turns out it wasn't compatible and it suspended my SIM/account for use on AT&T which was a pain to fix. Before I try to either try to get a refund from him or sell it to someone else, is there anything I can do? I know I read some stuff about cross flashing to other carrier software but that some stuff doesn't work and may stop working when AT&T drops 3G HSPA+ support in 2022.