US GSM & 3G Frequencies and.Two frequency bands are used by GSM service providers in the United States. At the inception of the GSM Network in the United States only 1900 MHz frequency was used for GSM cell phone service. For a while now there has been a growing amount of GSM service on the 850 MHz band especially by AT&T/Cingular. This type of service was at first developed for rural areas, because the 850 MHz band has better range than the 1900 MHz band. Now it's widespread in all areas.
Most of the 850 MHz service belonged to AT&T, and Cingular (these two companies have merged Cingular is being phased out). T-Mobile does not have any of its own 850 MHz service. It does have roaming agreement with AT&T. So T-mobile user will sometimes find themselves in an area where the only signal available is on 850 MHz and they can use their cell phones in these area’s where roaming charges usually apply.
Do you need both frequencies in the United States?No and Yes depending on the users situation. The user only need one of the frequency bands because the coverage is so wide spread that he/she will get service in most of the country. However it’s a good idea to have both bands in case of an emergency the user needs service and his/her phone can roam off the secondary band. But because these bands are used by competing service providers i.e. AT&T (formerly Cingular), T-mobile and others chances are that if there is service for one service provider in an area there will be service for other as well.
Which frequencies are used internationally?GSM was developed in Europe. Initially, all countries with GSM service used the 900 MHz band. Than service providers started to add 1800 MHz coverage, due to congestion in the 900 MHz band. Currently majority of the countries in the world use the 900/1900 MHz frequency. With the exception of the United States which stated off with the 1900 MHz frequency band and than added the 850 MHz as well. Some countries with close links to the United States also use the 1900/850 MHz frequencies.
If you plan on traveling overseas in the future refer to the table Below to get a feeling for which countries use which frequency bands. 900 MHz frequency band is the most common band used internationally. 1800 MHz frequency band will give users expanded coverage in countries that have 900 MHz frequency. Some countries only have 1900 MHz. Japan is the only county in the world that doesn’t have a GSM network it runs exclusive WCDMA/UMTS/3G. The Good news is that a lot of new Quad Band phones come with WCDMA/UMTS/3G built in along with the four GSM frequencies.