FYI: a "a1533" T-Mobile/at&t phone is GSM which means it can't be used on Verizon which is CDMA... however, a "a1533" Verizon CDMA phone can be used on a GSM network (except some 4g LTE) like T-Mobile/at&t because it is dual band... please correct me if I'm wrong...
I'm having a hard time understanding which network this phone works on. I've read so many different things. Which network did you use it on? That network should be guaranteed.