Hard to believe but the US government has now made it a federal crime to unlock a cell phone, as that act is no longer an exception to the DMCA beginning on Saturday, January 26. The reason for ending this exception is because the US Government doesn't believe consumers need to do so at this time, as they are of the opinion that there are now adequate ways to obtain an unlocked cell phone (either through the market pre-unlocked or via a wireless carrier). What's shocking are the enforceable penalties that can be imposed (not saying they will be but they are there.) First offenders face up to 5 years in prison and a $500,000 fine. Repeat offenders up the winnings to up to 10 years in prison and a $1 million fine. The words of the statute that provide for these penalties are attributable to someone who "willfully and for purposes of commercial advantage or private financial gain." So the way I read it, if you unlocked your cellphone in order to switch carriers and pay less for the services, you could be sentenced under the statute. While the cellphone police aren't breaking down your door, nobody knows how this one will ultimately play out. I doubt carriers will want to discuss the potential penalties except to say you shouldn't be breaking protective measures. Note: there is an exemption for phones purchased prior to this date and the amendment applies prospectively.
Here's an article by the EFF as to recent events and what it has done to keep jailbreaking from being illegal. Oddly enough, jailbreaking your tablet is still illegal.