Wife and I always buy our cells phones 1 to 2 years old, then have them assigned to our cell phone company.
I knew the technology would catch up sooner rather then later.
Our new phones are the Moto X Pure Edition (Pure Droid with some Motorola features). The main feature is Unlocked and can be used with ALL cell phone technology. This means GSM and CDMA. We have been using consumer cellar for the last year now tih no issue. MPE also has the Hot-spot which works very well.
If needed we can also go with Verizon on the BYOP program. I figured these phones should last well over 4 years, as that is how long we keep them