Mostly the Nexus 6P.... I hate not having it (I have two phones, iPhone 6s Plus on Verizon with unlimited data, and 6P on AT&T with unlimited international data). I read they won't allow it because "unlocked boot loader" but that sounds like B.S. to me. Every other carrier allows it, and if it was so bad, why would they even allow them on the network in the first place?
