Reach out to your provider to learn about its specific unlock policy. Most major mobile providers will unlock your phone as long as your contract is finished or you've paid the early termination fee to cancel your existing plan. They might also unlock your phone if you are travelling to another country and need to use a local carrier there.
Some companies are happy to unlock a phone if it is from one of their rivals. Reach out to your desired carrier and learn what their policy is.
Many phone manufacturers release unlock codes, which are very helpful if you are unlocking your phone on your own. You can run a Google search to find unlock codes for your phones make and model.
Check forums dedicated to cell phone unlocking. They are a great resource with a lot of people who are very knowledgeable.
If the above options dont appeal to you, there are also third-party sites and local retailers that specialize in unlocking phones
Regardless of which route you take, beware of one caveat
R SIM 9 PRO iPhone 5C,5S,5, 4S iOS7 Unlocking and Activation GSM/CDMA 2G/3G/4G ..
R-SIM9 PRO is first Universal Unlocking and Activation card for iPhone 5S/5C/5/4S mobile phones made by Apple. R-SIM9 PRO unlocking supports any baseband (both CDMA, GSM & CDMA), 2G, 3G, 4G sim cards and networks. Supports iOS 7. It comes with its NEW own interface, that is very simple and easy to use. All you need to do is insert R-SIM9 PRO into your iPhone, go to Settings > Phone > SIM Application and add the 7 digits IMSI of your iPhone carrier from the list below then restart.$3USD