from web site
In addition to giving a consumer the chance to check out any other network carriers, there is a number of other examples of why you may wish to factory unlock your cellphone before the end of your contract. You happen to be heading overseas for instance, you'll probably decide to make use of a domestic sim card when you're there to stay away from heavy roaming penalty charges. Or when you've decided to sell your phone then you'll probably get a higher price and more interest in a mobile phone which is free to make use of with any network carrier.
Absolutely nothing is unlawful about unlocking your cellular phone. It is your phone and you are obviously within your legal rights to use it with any carrier you choose. Nonetheless, there is a chance that network unlocking your cell phone is going to void your warranty, so it may very well be best to wait until you've finished your contract before deciding to leave your current carrier.
When your phone is unlocked, you are ready to find one of the least expensive mobile offers out there - a pay-as-you-go deal. Most of these usually operate on a rolling monthly basis, which means you can use the package for as long as you are satisfied with your mobile phone or you can up-date when a new handset is available or your trustworthy old mobile phone at some point gives up.
If you're unsure who to use, I highly recommend Unlock.Zone. They supply unlocks for all major manufacturers and networks, have a guaranteed price match promise, plus even more importantly, have a full refund policy in the unlikely event they can't unlock your mobile. I have used them myself personally and was really happy with the service I received and ultimately that they successfully unlocked my cellphone.
Here's a link to their home page: Phone Unlocking Service