In mobile phones, dual-band and tri-band refer to functionality that allows a cell phone to support either two or three frequency bands out of the four major GSM (TDMA) bands - 850/900/1800/1900 MHz.

GSM 900/1800 bands work in Europe, Africa, Asia, and Brazil
GSM 900/1800/1900 bands will work on at least one network in most countries around the world except for some networks that only support 850MHz(ATT in USA)

Please check with your local service provider regarding the frequency for your country.