You're talking about the ones on eBay?
As I understand it, the manufacturers send them to the phone companies "locked" to avoid theft and unauthorized usage. People on eBay buy them in similar lots and turn around and sell them. When they first started doing so, the phones were "locked," and nobody really knew it, until the customers complained that they couldn't use 'em. So now they make sure that they're "unlocked."
Once unlocked, you simply need to insert the SIM card from your old phone, and call your provider with the ID number of your new phone...usually located under the battery. Or, you can just take it to a local store, and have them do all that for you.
