The devices you buy from US mobile carriers are almost always locked to a single network, and unlocking them has been a legal gray area for the last few years. Now Congress is finally taking action to remedy that. The Unlocking Consumer Choice and Wireless Competition Act has been passed by the Senate, matching a House bill passed in February. As you can imagine, consumer rights groups are pretty jazzed.
It seems counterintuitive, doesn't it? You bought a device, but even if you pay full price, it's probably illegal to unlock it to use on another carrier. It all comes down to the Digital Millennium Copyright Act (DMCA) and its anti-circumvention provisions. Unlocking a phone could be considered breaking a "technological measure" as described by the law. It's akin to breaking a DRM system to use a digital file on unapproved platforms (which again, is kind of crazy). There was a brief time a few years back that unlocking was permitted by a Library of Congress exemption, but when the next review came up in 2012, the exemption was removed. So began the political wrangling to do something about it.
The House and Senate sponsors have been working together to ensure the differences in the bill can be reconciled and signed into law by the president quickly. The only significant sticking point is the removal from the Senate version of a ban on bulk unlocking for resale. That provision would be trouble for companies like Tracfone, which sells subsidized prepaid phones.
Carriers have recently adopted clearer policies on unlocking devices, but consumer rights organizations point out you shouldn't need permission from the carrier to unlock your phone. Hopefully you won't need to do that much longer. The pending legislation doesn't actually codify unlocking in the law permanently, but rather requires the Library of Congress to reinstate the exemption immediately and consider extending it when the next review comes up.