Band
In wireless communication, band refers to a frequency or contiguous range of frequencies. O2 and Vodafone work on the standard GSM900 and GSM1800 frequencies, whereas Orange and T-Mobile work on GSM1800 alone.
Most of the world uses 900/1800 MHz, but some (notably Canada and USA) operate on GSM1900. You will need a tri-band phone (900/1800/1900 MHz) if you want to use your phone in the Americas.
See also:
