An unlocked tri-band phone is a mobile phone that is open to using subscriber identity module (SIM) cards from any service provider and can support up to three different frequency bands. This allows owners to use their devices in regions with telecommunications systems that use the supported frequencies. An unlocked tri-band phone has the freedom to use the services of any provider within the supported areas, making it extremely flexible for roaming use. Frequent travelers often utilize the devices to get better service and lower communication costs in the different regions they visit.
Many service providers offer mobile phones with SIM locks, barring the user from using other SIM cards in their devices. Providers often use this feature as a means of ensuring users will continue to subscribe to their services and to offset the financial losses incurred if the phone was sold to the user at a lowered cost. Many users, however, see the SIM locking as a burden, especially if they become dissatisfied with their providers' service and would like to transfer to another one. If users have their phones unlocked, they can use SIM cards from any provider, giving them the power of choice.
The advantage is greatest, however, with unlocked tri-band phones. Mobile phones can only operate on a fixed set of frequencies, determined during manufacturing. Some regions use different frequencies than others; global system for mobile communications (GSM) 850, for example, is most popular in North America, whereas GSM 900 is used more frequently in Asia. Multiple-band phones are designed to function at multiple frequencies, allowing users to access networks in a greater selection of regions — the more bands supported, the more service areas are accessible. An unlocked tri-band phone has support for three frequency bands, making it usable in Africa, Asia, Europe, and in certain parts of North America.
An unlocked tri-band phone gives users a large amount of flexibility in the ways they use their phones and can create significant savings. A traveler, for example, can use a SIM card purchased at his destination and use it instead of paying his regular provider's roaming costs or purchasing a compatible phone. This strategy is often used by individuals who tend to go from one service region to another on a regular basis. The feature also gives the phone greater value on the secondary market; because it can be used in multiple regions and with any provider, the number of potential buyers is proportionally increased.