Quad band cell phones is standard for mobile phones supporting four frequency bands of GSM 850/900/1800/1900MHz. Generally speaking, Quadband phones can work in all GSM networks worldwide, no matter where they are located. Tri-band mobile phones describe those cell phones which support GSM900/1800/1900MHz. Mainly, GSM1900MHz is essential in the most phone carriers of U.S./Canada/Latin America and GSM850MHz is necessary in the most phone carriers of U.S./Canada/Latin America. Obviously, one quad-band phone must work properly in phone networks triband phones require, but not like that opposite as quad band networks cover tri-band networks, and triband networks are included in quadband networks.
However, if you are using AT&T Mobility in USA, onThesource.com highly suggests you would better buy quad band mobiles, or else, your future phone will display “emergency”. If your current SIM card belongs to T-Mobile in USA, you can both choose quad-band cell phones or tri-band mobile phones, because T-Mobile only requires GSM1900MHz, and quadband cell phone or tri-band cellular phone covers it already. Finally, quad band cell phone can roam in GSM networks all over the globe.