Reports are suggesting that Apple has removed the API interface that detects if an iOS device has been jailbroken in the latest version of the iOS software, 4.2. The original API appeared in iOS 4.0 but appears to have been taken out of the latest software.
Apple has traditionally been staunchly against jailbreaking from the very start, stating that users who do jailbreak immediately void the warranty for their Apple devices. When the US Government ruled that users were legally entitled to jailbreak their devices, Apple still maintained that they would not provide support for issues on jailbroken phones in their stores.
The removal of the jailbreaking detection API could mean one of two things. The first, and relatively unlikely reasoning, is that Apple has accepted that jailbreaking is a just a part of life and that inflicting such a strict walled garden of software on their mobile users is naturally expected to induce this behavior in a proportion of individuals. The second option is that Apple is making a big change.
The second option is that Apple is preparing to implement a completely new method of jailbreak detection either via a new, unseen API or via hardware detection. Naturally, it would be unseemly to suggest that Apple may have done this to irritate AT&T who restrict the use of FaceTime over their 3G network; jailbreakers of course can enable FaceTime over 3G.
Whatever the reason, hacking dev teams will be eager to look at the developer seeds of iOS 4.3 for iPhone, iPad and iPod to see which route Apple is taking.