Cell phone carrier providers in the US operate based on different technology, and may be of importance when choosing a phone. Most of the phone carriers in the world use GSM technology or Global System for Mobiles. If you are in the US, the major carriers that use GSM are Cingular (now AT&T) and T-Mobile. Sprint/ Nextel uses both CDMA and a proprietary system called iDEN and Verizon uses CDMA or Code Division Multiple Access.

Why is this important? If you travel abroad and would like to use your cellphone, you will need a GSM phone. Then you can just switch out the SIM card to a local one, activate service, and start talking! Of course, the phone has to be unlocked which is easily accomplished by calling your wireless provider and asking for the code. They will do this free of charge (although they are some PDA phones which networks are resistant to unlocking).

Also, a phone on Verizon's CDMA network will not work with TMobile's GSM service for example.

But, All GSM phones are not created equal. GSM technology operates on different frequencies. Most phones support at least three bands: 900/1800MHz (for Europe) and 1900MHz (for the USA). However, in the US, GSM carriers are now expanding their wireless coverage using the 850MHz frequency band. So you now need a quad-band GSM phone in order to get good coverage world-wide (850/900/1800/1900Mhz).

Although Verizon and Sprint use CDMA, there are some CDMA/GSM world phones out there, like the Samsung A790 and Nokia 6630.

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