HTC ONE M8 0P6B100 - FACTORY UNLOCKED
HTC ONE M8 HTC6525LVW - VERIZON
HTC ONE M8 P6B700 - SPRINT
HTC ONE M8 0P6B120 - AT&T
HTC ONE M8 0P6B130 - T-MOBILE
Factory Unlocked means that the phone isn't attached to any cell phone service and can be used with any service that uses a SIM card.