The DMCA provisions for circumventing an access control measure. Cell phone unlocking had an exemption before, but are restricted again.
I'm sure they wouldn't pursue it... but it's shitty enough that they could.
And even if those measures are protecting copyright in addition to locking down the device, has any court ever ruled on whether circumventing those measures without intending to breach copyright is a violation?
If a car manufacturer decided to lock the hoods of the cars they sell so that only authorized mechanics could access the engine, could they use the DMCA to outlaw users from circumventing the hood-locks on their own cars merely by printing some copyrighted text on the inside of the hood, and call it a copy-protection measure?
Auto manufacturers, along with printer manufacturers, are already using IP in the on board diagnostics and printer cartridges to claim copyright violations when people adjust or replace parts "without authorisation."
Regarding printer cartridges, there have already been court rulings [1] that have determined that "jailbreaking" them isn't a violation of the DMCA, making the distinction specifically on the basis of whether the the element of the product being protected is "creative" or "functional". So we already know from case law that the DMCA doesn't actually prohibit people from circumventing functional lock-outs.
[1]: http://en.wikipedia.org/wiki/Lexmark_Int%27l_v._Static_Contr...