what is Unlocked GSM phone?

GSM phones are available as "unlocked phones "and you can use new GSM phones without buying new service plans or without signing 2 year or 1 year agreement with provider liker Cingular, T mobile, verizon or sprint.

A GSM phone is not directly linked to you. Instead, it has a removable account card, called a SIM (subscriber information module) and this SIM has a unique serial number on it. This is what identifies you to the wireless provider.