Quad-band GSM refers to a device, such as a mobile phone, that operates on four different GSM frequency bands. The bands of operation are as follows: 

• 850 MHz [U.S./Canada/Latin America/Brazil (Brazil provided by Vivo)]
• 900 MHz [Africa/Europe/Brazil/Australia/Asia (Eastern Asia)]
• 1800 MHz [Africa/Europe/Australia/Asia/Brazil]
• 1900 MHz [U.S./Canada/Latin America/Brazil (Northeastern Brazil provided by Vivo)]

Sometimes referred to as "World Phone," the quad-band GSM technology is an upgrade to the tri-band technology which supports 850, 1800, and 1900 MHz bands. Although some phones designated "quad-band" support different frequency bands, very few use 450 MHz which is often employed in areas where posible users are spread over a large area due to the fact that a lower frequency inherently has a longer range. Though a quint-band GSM phone including the 450 MHz band in addition to the frequencies of quad-band is possible, there are no current announcements of such a phone.