Almost all the iPhones in circulation are factory locked devices. This means they were locked by Apple, at the request of the network that supplied the handset as is was sold at a heavily discounted rate. In every country that Apple offer the iPhone, they have signed agreements to supply locked handsets to the major cell phone networks. Accordingly, if you bought an iPhone for a fraction of the MRP from T-Mobile for example, if you try an AT&T SIM card in the phone you will get no service. The major carriers are so confident that they can recover the losses they incur supplying discounted iPhones, that they offer them at massively discounted rates to entice customers in. So confident are they that they will recover their money, there have been cases where some networks have been known to offer iPhones completely free of charge if a customer agrees to sign up to use it on their network for thirty six months.
Getting yourself an iPhone for cheap may sound like a great idea, but what if at some point in the future you want to move to a new network. What do you do with your iPhone then? It may be the case that the network you are with has very poor coverage in your area, or an alternative carrier is offering the same services for a lot less money.

Pre 2011 there were two methods available to unlock an iPhone. However in July of that year Apple patched the hole in the iPhones iOS that had enabled a software unlock to function. Although it was once possible to install software on to an iPhone to unlock it, Apple were successful in being able to block this process and it hasn't worked for several years now.

It is surprising but often people were unaware that software unlocking would void the manufacturer's warranty on their device and could only be applied to handsets running firmware 5.1.1 or earlier. Although there are still some devises out there that can be unlocked using this method (i.e. running iOS 5.1.1 or below), they are limited to certain mo