Tri- and quad-band cellphone designations refer to the 2G network.
As of the date of publication, mobile phones are capable of connecting to the 2G, 3G and 4G wireless networks using a variety of technologies on different frequencies. Phones that access the 2G network use GSM technology on the 850, 900, 1,800 or 1,900 frequencies. Tri-band phones use three of these frequencies, while quad-band phones use all four.
Tri-Band
With its ability to connect to three of the four major GSM frequencies, a tri-band phone works in most parts of the world. The 850 and 1,900 frequencies are used in the Americas, while the 900, 1,800 and 1,900 frequencies are supported in most other parts of the world. These differences divide tri-band mobile phones into two categories: the Americas and European. European tri-band phones provide complete coverage in Africa, Asia and Europe and work on at least one network in the Americas. Americas mobile phones operate in the same manner, but in reverse order. Because they support just three of the major GSM frequencies, there are parts of the world a tri-band phone will not operate.
Quad-Band
Unlike a tri-band mobile phone, quad-band phones support each of the four major GSM frequencies and, because of this, provide complete coverage in all parts of the world. Quad-band and tri-band phones use one of two technologies to transfer data to and from the 2G network: Enhanced Data for Global Evolution and General Packet Radio Service. Because these technologies provide faster data transfer rates than previous 2G network technologies, they are often referred to as "2.5G" network technologies.
GPRS
Tri- and quad-band phones use GPRS technology for any network connection that is not for voice or text transmissions. In theory, GPRS transfer speeds are capable of reaching speeds of up to 115 kilobits per second, but realistic estimates put the speeds in the 30 to 40 Kbps range. GPRS-equipped phones, such as tri- and quad-band, are constantly connected to the 2G network and the Internet, so services are easily and quickly accessed when they are needed. GPRS is a packet-switching technology which transfers data in addressed packets, or very small pieces, which occupy network space only while that packet is being transmitted. This is an improvement on previous circuit-switching technologies, which required a dedicated connection before data was transferred.
EDGE
Based on GPRS technology, EDGE technology is used by default for all 2G network transmissions, such as those generated by tri- and quad-band phones. EDGE is capable of data transfer rates of up to 246 Kbps, but most EDGE networks are equipped to only handle 135 Kbps. When EDGE is not available, tri- and quad-band phones will automatically switch to GPRS for transmitting data.
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