Most cell phones are locked, meaning that the phone is tied to a certain carrier's cellular service. To use that phone with another carrier, you need to unlock it. Unlocking your phone can be risky business -- doing so may void any warranty you have, and can irreparably harm your phone.
Still, plenty of people are interested in unlocking their cell phones. If it works, unlocking your phone gives you more freedom in how you use it. You may be able to make cheaper calls, install new software, and simply do more with your phone when it's unlocked.
Listed below are some software programs designed to help you unlock your Samsung phone. Note that I have not tried any of these apps and cannot vouch for their performance. And it's worth noting, once more, that unlocking your phone can severely damage it.
Buying an unlocked phone can be a safer (though more expensive) alternative to unlocking a phone yourself. For more information, read my complete guide to buying and using an unlocked phone.