There are various methods to network unlock your Iphone such as using software,remote unlocking method and so on.. If you have bought the Iphone5 after jan 26 2013 it is illegal to unlock without network provider permission. If you want to make it legal you have to sign a petition in the Link below. https://petitions.whitehouse.gov/pet...legal/1g9KhZG7
It has to be done by 23rd of February .To make it legal you need to wait until 1 lakhs petition to be signed in and approved by USA government .later on you can unlock it.
If that is not your case and if it has been purchased before that date then there is no legal issues.Here is a site where you can get your Iphone unlocked using remote unlocking service ClassicUnlocking.com .Further you can unlock it to any gsm network it has been locked to.