[LG Optimus 4X HD] RuedasLocas:
Extracted from Wikipedia: http://en.wikipedia.org/wiki/GSM_frequency_bands

For those who have doubts and are a little lazzy to search, here you can get some info :o

GSM-900, GSM-1800 and EGSM/EGSM-900

GSM-900 and GSM-1800 are used in most parts of the world: Europe, Middle East, Africa, Australia, Oceania (and most of Asia). In South and Central America the following countries use the following:

Peru – GSM-1900

Costa Rica – GSM-1800

Brazil – GSM-850, 900, 1800 and 1900

Guatemala – GSM-850, GSM-900 and 1900

El Salvador – GSM-850, GSM-900 and 1900

Venezuela – GSM-850, GSM-900 and 1900

GSM-900 uses 890–915 MHz to send information from the mobile station to the base station (uplink) and 935–960 MHz for the other direction (downlink), providing 124 RF channels (channel numbers 1 to 124) spaced at 200 kHz. Duplex spacing of 45 MHz is used. Guard bands 100 kHz wide are placed at either end of the range of frequencies.[2]

GSM-1800

GSM-1800 uses 1,710–1,785 MHz to send information from the mobile station to the base transceiver station (uplink) and 1,805–1,880 MHz for the other direction (downlink), providing 374 channels (channel numbers 512 to 885). Duplex spacing is 95 MHz. GSM-1800 is also called DCS (Digital Cellular Service) in the United Kingdom, while being called PCS in Hong Kong[3] – not to mix up with GSM-1900 which is commonly called PCS in the rest of the world. Mobile Communication Services on Aircraft (MCA) uses GSM1800.[4]

GSM-850 and GSM-1900

GSM-850 and GSM-1900 are used in Argentina, Brazil, Canada, the United States and many other countries in the Americas.

GSM-850 uses 824–849 MHz to send information from the mobile station to the base station (uplink) and 869–894 MHz for the other direction (downlink). Channel numbers are 128 to 251.

GSM-850 is also sometimes called GSM-800 because this frequency range was known as the "800 MHz band" (for simplification) when it was first allocated for AMPS in the United States in 1983.

The term Cellular is sometimes used to describe the 850 MHz band, because the original analog cellular mobile communication system was allocated in this spectrum.

GSM-1900 uses 1,850–1,910 MHz to send information from the mobile station to the base station (uplink) and 1,930–1,990 MHz for the other direction (downlink). Channel numbers are 512 to 810.

PCS is the original name in North America for the 1,900 MHz band. It is an initialism for Personal Communications Service.

GSM-450

Another less common GSM version is GSM-450.[5] It uses the same band as, and can co-exist with, old analog NMT systems. NMT is a first generation (1G) mobile phone system which was primarily used in Nordic countries, Benelux, Alpine Countries, Eastern Europe and Russia prior to the introduction of GSM. It operates in either 450.4–457.6 MHz paired with 460.4–467.6 MHz (channel numbers 259 to 293), or 478.8–486 MHz paired with 488.8–496 MHz (channel numbers 306 to 340). The GSM Association claims one of its around 680 operator-members has a license to operate a GSM 450 network in Tanzania. However, currently all active public operators in Tanzania use GSM 900/1800 MHz. Overall, where the 450 MHz NMT band exists, it either still runs NMT, or its been replaced by CDMA. GSM-450 is a provision; it has not seen commercial deployment.

GSM frequency usage around the world

The Americas

In North America, GSM operates on the primary mobile communication bands 850 MHz and 1,900 MHz. In Canada, GSM-1900 is the primary band used in urban areas with 850 as a backup, and GSM-850 being the primary rural band. In the United States, regulatory requirements determine which area can use which band.

GSM-1900 and GSM-850 are also used in most of South and Central America, and both Ecuador and Panama use GSM-850 exclusively (Note: Since November 2008, a Panamanian operator has begun to offer GSM-1900 service). Venezuela and Brazil use GSM-850 and GSM-900/1800 mixing the European and American bands. Some countries in the Americas use GSM-900 or GSM-1800, some others use three: GSM-850/900/1900, GSM-850/1800/1900, GSM-900/1800/1900 or GSM-850/900/1800. Soon some countries will use GSM-850/900/1800/1900 MHz like the Dominican Republic, Trinidad & Tobago and Venezuela.

In Brazil, the 1,900 MHz band is paired with 2,100 MHz to form the IMT-compliant 2,100 MHz band for 3G services.

The result is a mixture of usage in the Americas that requires travelers to confirm that the phones they have are compatible with the band of the networks at their destinations. Frequency compatibility problems can be avoided through the use of multi-band (tri-band or, especially, quad-band) phones.

Africa, Europe, Middle East and Asia

In Africa, Europe, Middle East and Asia, most of the providers use 900 MHz and 1800 MHz bands. GSM-900 is most widely used. Fewer operators use DCS-1800 and GSM-1800. A dual-band 900/1800 phone is required to be compatible with almost all operators. At least the GSM-900 band must be supported in order to be compatible with many operators. However, Thailand has also approved for some time now the use of the GSM-1900 band in an attempt to alleviate network congestion.

Multi-band and multi-mode phones

Today, most telephones support multiple bands as used in different countries to facilitate roaming. These are typically referred to as multi-band phones. Dual-band phones can cover GSM networks in pairs such as 900 and 1,800 MHz frequencies (Europe, Asia, Australia and Brazil) or 850 and 1900 (North America and Brazil). European tri-band phones typically cover the 900, 1800 and 1900 bands giving good coverage in Europe and allowing limited use in North America, while North American tri-band phones utilize 850, 1,800 and 1,900 for widespread North American service but limited worldwide use. A new addition has been the quad-band phone, also known as a world phone, supporting all four major GSM bands, allowing for global use (excluding non-GSM countries such as Japan or South Korea).

There are also multi-mode phones which can operate on GSM as well as on other mobile phone systems using other technical standards or proprietary technologies. Often these phones use multiple frequency bands as well. For example, one version of the Nokia 6340i GAIT phone sold in North America can operate on GSM-1900, GSM-850 and legacy TDMA-1900, TDMA-800, and AMPS-800, making it both multi-mode and multi-band. As a more recent example the Apple iPhone 5 and iPhone 4S support quad-band GSM at 850/900/1,800/1,900 MHz, quad-band UMTS/HSDPA/HSUPA at 850/900/1,900/2,100 MHz, and dual-band CDMA EV-DO Rev. A at 800/1,900 MHz, for a total of 'six' different frequencies (though at most four in a single mode). This allows the same handset to be sold for AT&T Mobility, Verizon, and Sprint in the U.S. as well as a broad range of GSM carriers worldwide such as Vodafone, Orange and T-Mobile (Excluding-US), many of whom offer official unlocking.

Note that while the Nexus One, like many other devices on the market, may also become available in a UMTS I/II/IV or 2,100/1,900/850 MHz combo,[7] it would still be considered tri-band UMTS, not quad-band, as the hardware is limited to supporting any three bands at one time. Further, as HSPA runs atop UMTS, it would not be considered a "mode" by strict definition.