The following is a summary of info gleened from a few pages on the web. You can find the same and more by doing a search at your favorite search engine. Enter the serch string: "unlocked cell phone"
GSM cell phones are designed to work with any service provider.
When originally manufactured, all GSM cell phones are unlocked. That is, they can be used with any SIM from any cellphone service provider - always assuming, of course, that the cellphone service provider has compatible GSM service on the same frequency bands that the phone can operate on.
A locked phone, will only recognize a SIM card from a particular carrier. If the cell phone is unlocked, it will recognize a SIM card from any carrier. The "lock" is a software setting that keeps the cell phone "loyal" to one carrier.
One way to get an unlocked phone without proprietary settings is to buy it new from a third party vendor in its original, unlocked state. The downside is that the price is commonly close to full retail. Some consumers might find it tough to dish out big bucks for a phone that they can get for free with a plan. The advantage is that the third party unlocked phone should work equally well with any carrier that uses SIM cards.
Carriers operating on the GSM network use SIM cards. In the United Sates, this includes Cingular Wireless, now one with AT&T Wireless, and T-Mobile. Carriers that use the competing CDMA network do not yet use card-enabled phones. These carriers include Sprint PCS, Verizon and Virgin Mobile. The CDMA equivalent of the SIM card — the R-UIM — will be used by these carriers in the future.
Visit the CTE Online Store to shop for an Unlocked Cell Phone. Or use one of the links below to check out other areas of Keith's web site.