Usually when you get a cell phone from a carrier it is "locked" to that carrier. Basically, this means that a phone you get from Verizon or Virgin, or Rogers (or whoever your cell phone provider is) they program the phone to only work with their service. The phone is "locked" as a Verizon, etc only phone. An unlocked phone is when this programming is removed, and a phone that is "unlocked" can be used with any carrier (with exceptions).