Activating an unlocked iPhone on the CDMA side can be a trick. I would avoid it. If you are going to go forward, look at beigephone which activates difficult CDMA phones on PagePlus's MVNO of Verizon. E.g. you get the Verizon network but PagePlus provides the service.

On iPhone just remember that LTE has more flavors than Baskin Robins (an ice cream chain known for its many flavors). Buying it off the net might be a chore, but the knew Google Nexus 4 is about $350 and is a pentaband worldphone with great features and completely unlocked. Unfortunately, it will be hard to get in brick and mortar stores.

http://www.google.com/nexus/4/

You can use the phone on TMobile or ATT at HSPA+ speeds (no LTE support), will support VOIP Over 3.5G, has a great navigation system, Google Now,and no carrier bloatware.