In the United States, where cell phone carriers frequently offer cheap or free phones as incentives to draw customers, cell phones are typically "locked" so that they can only be used with that particular carrier. However, in most other countries, especially in Europe and Asia, unlocked cell phones are the norm. For Americans who travel internationally, an unlocked cell phone allows them to purchase prepaid local service to make and receive calls inexpensively.
GSM vs. CDMA Networks
Cell phones that run on the GSM (Groupe Speciale Mobile or Global System for Mobile Communications) network use SIM (Subscriber Identity Module) cards to store the user's personal information and cell phone settings. SIM cards are interchangeable from one unlocked cell phone to another. In the United States, two major American mobile phone providers, T-Mobile and AT&T run on the GSM system. Their cell phones use SIM cards.
Prepaid SIM cards for individual countries or for general international use are relatively inexpensive and allow the user to make and receive calls economically when traveling internationally. Most of the world's cell phones use the GSM network.
Most cell phones in the United States run on the CDMA (Code Division Multiple Access) network, which do not use SIM cards. However, in the future, R-UIM (Re-Usable Identification Module) cards, in use in China since 2002, promise to make interchangeability possible for CDMA network cell phones in the United States. In the United States, Verizon Wireless, Sprint Nextel and a number of regional carriers such as Alltel and U.S. Cellular use the CDMA network.
Using Unlocked Cell Phones Internationally
Unlocked cell phones that run on the GSM network can be used with any carrier, domestic or international, as long as the proper SIM card is inserted and the cell phone has the capability to transmit along the band wavelength of the country where the caller is located. GSM carriers in the United States, Canada and many parts of Latin America use the 1900 and 850 bands. The 1900 band is used in concentrated urban and developed areas, while the 850 band is frequently used in more remote areas. Two other bands, 900 and 1800, are used throughout Europe and in much of the rest of the world. A quad-band phone supports all four bands and will work nearly everywhere. Less expensive tri-band cell phones generally support the 1900, 850 and 1800 bands and are sufficient for travel in the United States and Europe.
Purchasing Unlocked Cell Phones
Presently all unlocked cell phones in the United States use the GSM network. Cell phone service providers almost never sell unlocked phones, but third-party retail outlets often do. Several online outlets also sell unlocked cell phones, including Amazon.com. Another reputable online dealer is Telestial, which also offers prepaid SIM cards and international calling cards along with unlocked cell phones. It is also possible to purchase unlocked cell phones when traveling overseas, particularly to Europe and Asia. However, prices are often very high, especially for sophisticated multi-featured models.
Unlocking a Cell Phone
It is also possible to have one's own cell phone unlocked to use with multiple carriers or with prepaid SIM cards, if it uses the GSM network, though the process is often tricky and may be expensive. Worse, if not done correctly the phone may become unusable. Some cell phone service carriers will unlock cell phones for customers upon request, especially after the expiration of initial contract periods. A number of free and paid unlock codes are available online, although it's wise to check out any Internet retailer before sending any money or providing a credit card number.
Considerations
The two cell phone networks, GSM and CDMA, are incompatible with one another. Consumers should keep this in mind when considering a change in cell phone providers.
Since unlocked cell phones must nearly always be purchased through retail outlets, the price is often prohibitively high. In addition, some or many of the advanced features of an unlocked cell phone may work differently than they would with a cell phone programmed by the carrier, or not at all. Before purchasing an unlocked cell phone for international travel, be sure that the phone supports the band(s) used in the country or countries planned for visits during the trip.
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