Earlier this year, because of the decision of the Library of Congress to not extend the protection for unlocking devices in the DMCA law, it became illegal to unlock your own device. This is just unacceptable given that you own the device, and many people have signed up the petition to the White House, passing the just then raised minimum of 100,000 signatures, while many in Congress have asked for changes to the law, too. FCC is now giving the carriers the opportunity to set their own standard policies, that would make it very easy for their customers to unlock their devices.
These are FCC's requirements:
1. A clear, concise, and readily accessible policy on unlocking.
2. That wireless companies agree to unlock mobile wireless devices for customers, former customers, and legitimate owners when the applicable service contract, installment plant or ETF [early termination fee] has been fulfilled.
3. Wireless providers will take the proactive step of notifying customers when their devices are eligible for unlocking and/or automatically unlock devices when eligible, without an additional fee.
4. That carriers will either process unlocking requests or provide an explanation of denial within two business days.
5. Providers will unlock devices for military personnel upon deployment.
Apparently, the carriers aren't exactly happy with them, especially with the policy #3, which would require them to notify their customers when their devices are eligible for unlocking, which suggests that to have it unlocked, you need to be "eligible" in the first place. That means that if you buy your phone on contract, you can't unlock it and use another carrier's SIM until your contract has expired.
That doesn't make much sense, considering that just because you unlocked your phone to use it with another SIM, doesn't mean you're just going to stop paying your contract. What it means is that you want to be able to switch between 2 contracts on the same phone, or you want to use it with some prepaid SIM, either in US or abroad.
The only reason the carriers don't want to agree to that very reasonable request in the first place, is because they are being anti-competitive, and want to keep you locked-in on their network for as long as possible, and they'd rather not have you go around and try other carriers' services.
The carriers have until December this year to agree with the above 5 requests, voluntarily, or they risk further regulation from FCC (which would probably be preferable, since the carriers barely respect FCC's regulations as they are, let alone having to respect the voluntary ones).