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Compatibility in the United States:
Tri-band (GSM 900/1800/1900) phones can be used with service providers providing the GSM 1900 in the United States (T-mobile). In addition, AT&T (Cingular) provides GSM 850 and GSM 1900. Therefore, there will be no network/signal in the area with only GSM 850 or without GSM 1900 frequency. Please contact your service provider for GSM roaming/frequency coverage prior to purchasing a tri-band phone.
Quad-band (GSM 850/900/1800/1900) phones can be used with any service providers issuing sim-card, such as T-mobile or AT&T (Cingular) in the United States, but not Verizon, Nextel, or Sprint.
Frequency-compatibility problems - GSM networks operate in four different frequency ranges (850/900/1800/1900). GSM-900 and GSM-1800 are used in most parts of the world (Europe, Asia, and Americas). GSM-850 and GSM-1900 are used in the United States, Canada, and many other countries in the Americas. The result is a mixture of usage that requires customers/you to confirm that the phone you have is compatible with the frequency of the network at your destination. Frequency-compatibility problems can be avoided through the use of multi-band, tri-band, or especially quad-band, phones.
- European tri-band phones typically cover the 900, 1800 and 1900 bands giving good coverage in Europe and Asia and allowing limited use in North America.
- Quad-band phones support all four major GSM frequency groups (850/900/1800/1900) for widespread usage globally.
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