Unlocking is the removal of SIM restrictions on the modem, allowing the use of the iPhone on any carrier. The main reason to unlock your iPhone is if you want to use it with a different service provider (ie T-Mobile). Here are 2 articles you may want to look at:

• What is unlocking an iPhone?
• The difference between jailbreaking and unlocking

There are two ways to unlock an iPhone. You can either do a software unlock, which usually requires some kind of hacking, or you can do a factory unlock.

Official Factory Unlock for iPhone

The difference between a locked iPhone and an officially unlocked one relies on the addition of the device’s IMEI number to a database of officially unlocked iPhones. The IMEI is like a fingerprint, completely unique to your device. When officially unlocked, your IMEI is added to an Apple database which authorizes the device for unlocking. There are now a few providers that have access to Apple’s database and offer permanent unlocks for a small fee.
The main benefits of a permanent IMEI unlock are:

• it’s simple, and official (registered as officially unlocked in Apple’s database)
• it works with any iPhone (unlock iPhone 2G, 3G, 3GS, 4, 4S, and iPhone 5)
• it’s 100% guaranteed to unlock your iPhone
• the iPhone can’t be locked again, even if you update your device in iTunes
• it does not void your iPhone warranty
• no jailbreak or hacking required

For those of you looking for a permanent IMEI factory unlock for your iPhone, we recommend using the services of Chronic. From our own experience, Chronic has been very professional. He offers fast, affordable and reliable official factory unlocks for iPhone. Please click here to refer to his website for pricing information. To our knowledge, this is currently the best way to permanently unlock an iPhone, especially since there is no software unlocks available for the latest iOS versions.

Software Unlock

This page is a reference guide for anyone looking to unlock the iPhone using software. Simply look for your firmware version and your iPhone model, then click on the appropriate tutorial. Note that at this time, software unlocks only work with older iPhone models that haven’t been updated to the latest software. If you’re looking for a reliable, permanent unlock, we can only recommend you do a factory unlock of your device (see details above).

Unlock iPhone : 4.3-6.1

http://devicesolver.blogspot.in/2014/02/ultra-snow-for-ios6.html