It looks like starting today it's going to be illegal to unlock your phone in the US. Apparently, the DMCA (Digital Millennium Copyright Act) prevents American from doing this.
Now you need to ask your carrier first before you can unlock.
Unlocking a phone has been part of the phone industry for years. I remember unlocking my Nokia 5190 around 10 years ago. So, it's a bit of a joke that it's now illegal.
Mind you, in the US there isn't a great deal of mobility between carriers because each carrier uses either a slightly different technology and or frequency. Still, it prevents you from moving to a carrier's MVNO.
So, if you unlock your phone now will some Jack Bauer type kick down your door?
If you think this is wrong/ridiculous/stupid/outrageous/etc make sure you sign the petition here.