A "locked" cell phone is set up to only recognize SIM cards from a specific service provider. They do this to ensure users will pay back their contract, which helps subsidize the phone. However, if you want to use more than one provider, you will need to unlock your phone. This is different from rooting or jailbreaking a phone, which only allows unofficial programs from being installed.
If you are looking into buying a new phone, there are a number of online stores that specialize in unlocked phones. These can be used with SIM cards from your service provider.
Talk to your provider first: under certain circumstances, they may help you unlock your phone. Most companies will let you unlock a phone you paid full price for, or you have paid by completing your contract.
You will probably need to know the serial number of your cell phone. This very long number is printed on the label underneath the battery, or can be displayed by typing *#06# into your phone.
There are many free sites that publish unlocking codes. http://www.unlockitfree.com/ covers Nokia phones, and http://mobile-cellphones.blogspot.com/ covers a wide variety of phones, but isn't serial number specific requiring you to enter in several codes to find the one for your phone. If you can't find a code here, do some web searching for your specific model. You should never need to pay for an unlock code.
Once you have the code, turn off your cell phone and remove the SIM card. Turn the phone back on. You'll see an error message. Type in the unlock code. If you are successful, you'll see a message saying something like "SIM is not restricted" or "Restriction Off." You can now use any SIM card with your phone.
Posted 3833 day ago