The Librarian of Congress ruled in October of 2012 that certain actions involving mobile phones were illegal under the Digital Millennium Copyright Act. The rules were revised to state that while it is legal to jailbreak smartphones, it is illegal to jailbreak tablets and illegal to unlock phones without permission from your wireless provider. A 90-day window was put in place that allowed consumers to purchase a phone and unlock it, however that window closes on January 26th. Note that jailbreaking is different from unlocking. Jailbreaking opens the phone up to run additional software. That will still be legal for smartphones after January 26th. Unlocking removes the restriction tying a phone to a particular carrier freeing the user to use a carrier of their choice.
However, the deadline is meaningless to some. For example, both Apple and Verizon sell unlocked iPhone 5s for a hefty unsubsidized price while AT&T will unlock a phone once it is out of contract. In any case, if you want to legally unlock your smart phone, now is the time to do it legally.