Thanks to edits made to DMCA exemptions back in October, it will be illegal for you to unlock your phone without the consent of the carrier starting tomorrow, January 26. From then on, you’ll have to ask your carrier to unlock your phone if you want to use it on another network, which seems a lot like pulling teeth. Even if your contract runs out and you're cut loose, no such luck will be granted.
The Library of Congress decided that third-party unlocking was no longer allowed, but decided to provide a 90-day grace period for which devices bought within the period could still be unlocked by anyone as usual, but tomorrow marks the end of that grace period, and the law will be in full effect.
Of course, these changes won't take away your ability to unlock phones, but it'll give carriers the upper edge when it comes to keeping their phones on their networks, meaning that if they catch you with an unlocked phone, they can turn you in, and carriers usually never want to unlock their devices, so good luck getting legal permission to do so.
So if you've been planning to unlock your smartphone, today is the day to do it before the swift hammer of justice comes down on you. Of course, you could still unlock it yourself after tomorrow, but there's always the chance that carriers will catch you, similar to how downloading copyrighted material is -- getting caught is always possible.