has been investigating the issue and concludes that Apple might have in fact violated the Magnuson-Moss Warranty Act:

It is questionable if Apple can simply word in their warranty agreement that SIM unlocks are a voiding condition. This would be necessary for Apple to legally void warranties based on a SIM unlock, and under Magnuson-Moss, any term of iPhone’s warranty that does so must be explicit and easy for the consumer to understand. Magnuson-Moss is vague on the implications of such a situation.

It would be similar to stating that using a third-party ink jet cartridge voids the warranty of a printer. While Apple makes the statement of "a product or part that has been modified to alter functionality or capability without the written permission of Apple…" voids the warranty, SIM unlock processes that are free and openly sourced, are not salient products, nor are they traditionally defined as a part. Furthermore, the SIM unlock can be reversed, and thus is not a permanent modification… in other words, Apple can remove it easily. Furthermore, any iPhones unlocked before said wording would still be entitled to warranty care… and Apple has no way of detecting exactly when an iPhone was unlocked.”

Also, there is a question regarding whether Apple’s update damages the iPhones on purpose of not. While Apple is most-likely to stated that such an effect was caused unintentionally, the law requires that the company prove it beyond any doubt.

However, if the iPhone was rendered useless on an intentional basis, then Apple faces an already lost battle, since such an action is clearly against the law.

All in all, there has been no lawsuit filed up to this point. Still, many users are likely to find (if they haven’t already) that their iPhones won’t work after the update and that spell a huge PR problem for Apple.