The term is used for Global System for Mobile Communication. It is a worldwide accepted cellular network standard which uses a SIM (Subscriber Identification Module) card to make and receive calls and data over the network. The SIM card holds the phone number assigned by the service provider, your phonebook and other registration information. GSM standard is used by approximately 213 countries with over 3 billion people. GSM network uses four frequency range 850 MHz, 900 MHz, 1800 MHz and 1900 MHz.
Tri-band Cell Phones
These phones will work around the world including United States and Canada but will not work with the service provider that only supports 850 MHz frequency.
Frequency Operation Mode: 900 MHz, 1800 MHz and 1900 MHz.
Countries: Europe, Africa, Asia, nearly all of United States, Australia and New Zealand.
Quad-band Cell Phones
Quad band phones will work all over the world with all GSM service providers.
Frequency Operation Mode: 850 MHz, 900 MHz, 1800 MHz and 1900 MHz.
Countries: Europe, Africa, Asia, United States, Australia, New Zealand, South America and almost all the countries
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If you are purchasing a Cell Phone check the above frequency band and make sure that the cell phone band is supported in the country. United States support 850 MHz and 1900 MHz frequency band. Majority of carriers in US such as T-Mobile, Cingular uses 1900 MHz frequency and in some state Cingular uses 850MHz frequency band.
What is Unlocked GSM Cell Phones?
Most cell phones service provider companies such as T-Mobile, Cingular etc provide cell phones to users which are network locked. This means that, the phones can only be worked with their company’s network.For example, a locked phone from T-mobile wouldn’t work with Cingular’s service. So if you want to use your cell phone anywhere in the world with any service provider you have to purchase unlocked cell phones which are not Network Locked by any service provider and you have to just transfer your existing SIM card into your new unlocked phone and your phone is all set to make and receive calls.