Commonly, an unlocked cell phone is a GSM-device (a phone with SIM card slot), that is not tied to a specific carrier. However, it’s easier to begin by explaining what a locked phone is.
High-end smartphones are very expensive. Traditionally, carriers do the next. They subsidize the purchase price in exchange for one or two-year contract. They suppose to regain the subsidy over the course of the contract. They put a lock on the smartphone. The lock is usually a software code. Due to that code, the device can’t be used on any other operator's network.
You buy that locked phone for the essentially low price. Even two or three times as low! But you will have to wait until the period of the contract expires before you can purchase another phone.
If you often travel and wish to use a local carrier instead of paying expensive roaming fees, the lock software will reject it. Passingly, switching a SIM card from a different carrier is a way to check out if your handset is locked or not.
In contrast to locked phones, an unlocked phone doesn't have the lock software on it; or you are able to get a code that unlocks the software.
How do you unlock a cell phone? To get your phone unlocked, you'll need to contact the cell phone company where your phone was purchased and ask for the SIM unlock code. Each cell phone carrier has its own guidelines for unlocking phones. But firstly get to know if your phone will actually be capable of functioning on another carrier before unlocking it.
Once a device is unlocked, it’s no longer bound to a specific carrier.
Then you are free to switch SIM cards from different wireless telecom networks at will and get service. Particularly, while traveling overseas, you always can purchase a local SIM card with a local call plan at your destination for making calls, texting, and surfing the Internet.