What is an unlocked cell phone? Traditionally, when you buy a cell phone and service plan from a mobile telecommunications carrier such as Sprint, Cingular or T Mobile, the phone is 'locked' within the network. In other words, that particular phone will not work should you decide to change carriers. For example, someone who uses Cingular cannot walk into a Sprint store and ask to change to a Sprint service plan without purchasing a new phone. Because U.S. carriers work off individual networks, transferring service and changing phones has been a challenge, until now.

The competition among cell service providers is fierce--and most of the companies are continually trying to pull customers from other networks. Before unlocked cell phones, switching carriers meant switching phones. So even if you had a fully-functional cell phone, you'd need to buy a new one once you changed providers.

Now, you can buy an unlocked cell phone. This means that you can switch providers at any time and keep the same phone. If you didn't purchase an unlocked cell phone, you can call the customer service department of your existing carrier and ask them to unlock the phone for you.

If you're planning on traveling overseas, you may want to invest in a GSM unlocked cell phone. GSM, or global system for mobile communications, ensures that your phone will work on overseas networks. An unlocked phone will allow you to insert any SIM card into the phone and then enable that phone to pick up local network service.