I just love this ongoing cat-and-mouse game – the minute a new update appears from Apple, the reply comes back from iPhone unlockers, and, believe me, there are a few of them out there. The U.S. Library of Congress has decreed that users, who choose to unlock their mobile devices for use on alternate networks, can not be prosecuted under the ‘Digital Millennium Copyright Act’ (DMCA), because there was, unfortunately, no requirement for companies to lock their phones in the first place.

The last round has gone to the ‘mouse’, because everyone has their iPhone ‘jailbroken’, right? And because everybody does that, then this is not a big deal. Until Apple reacted by tweaking the implemented locking mechanism with each new release of iOS, and, true to form, they did just that again with their new release at the beginning of the week.

Starting with iOS 4.2.1, the main part of the operating system will check the Baseband firmware at start-up to ensure that it matches an expected signature. If not, you will have a problem, because the phone will just not boot, in which case, you have to restore the phone to its original state – otherwise your iPhone remains stuck in recovery mode.

The Baseband firmware is that portion of the iOS actually controlling the cellular radio hardware, and it is necessary to hack this to allow your iPhone to be used on carriers other than AT&T.

This time Apple has done their homework and left some new problems for developers. However, the answer will, as always, come soon. In the meantime, those who are using their iPhone on carriers other than AT&T will just have to sit tight with their iOS 4.1 (or earlier) phones – for now.