The term “unlocked” refers to GSM phones that have been universalized, or unlocked, so that they may be used on a variety of cellular phone companies that use GSM, as opposed to simply one. In areas like the United States where cellular carriers offer free or deeply discounted phones with cell plans, the phones are commonly locked so that they will not work with other carriers. Once unlocked, however, the phone should work with any GSM carrier once a SIM card has been inserted into phone.