In reading or talking about digital wireless telecommunications, you often see reference to quad-band phones in marketing materials and specification sheets. What the term quad-band refers to are the frequencies on which the telephone operates. Cellular telephones as we know them today are, after all, the result of the marriage of the technologies of Alexander Graham Bell's telephone and Nikolai Tessla's radio.

Quad-band Phones and Digital Wireless

Radio waves travel on channels, or frequencies. The digitized analog signals of wireless phones do as well. There are three types of digital phone technology--TDMA (time division multiple access), CDMA (code division multiple access), and GSM (global system mobile communications). These technologies operate, depending on where in the world you are, on different frequencies. Cell phones are thus limited to specific regions.

All three technologies are used in the United States. The rest of the world uses only GSM. Unfortunately, the U.S. frequencies for GSM are not the same as those elsewhere. There are thus four frequencies used. In the United States, there are 850 MHz and 1900 MHz. In the rest of the world, there are 900 MHz and 1800 MHz. Quad-band phones support all four available frequencies and can, technically, operate anywhere in the world. This is their special appeal.

It is important to note that the quad-band capability is built in during initial manufacture, rather than being a feature that can be added by coding later on. Quad-band phones are also manufactured to accommodate the two methods by which cellular phone service providers link a subscriber to the network. In the United States this is achieved by hard coding the phone. Elsewhere a removable SIM--subscriber identification module--chipset is used.