An inside source at AT&T told MacStories that Apple is planning to release iOS 4.2, a major OS update for iPhones, iPods and iPads, on Friday November 12th at 10 AM PST. We also learned that updates to iTunes and Mac OS X will be released sometime tomorrow – iTunes will be reaching version 10.1 and Mac OS X will jump to the long-awaited 10.6.5 version.

Many users expected iOS 4.2 to be available today: iOS 4.2, however, depends on iTunes 10.1 and Mac OS X 10.6.5 for its AirPlay and AirPrint functionalities, respectively. According to our source, 10.6.5 completed the certification stage a few hours ago and iTunes was ready 3 weeks ago – likely after the release of beta 2 to developers.

We will keep you posted as we find out more. As noted by 9to5mac, German blog iFun discovered last week that Apple will push iPhone carrier updates on Friday, November 12th.

Update: We’ve got some more details to share. According to our source, AT&T staff is required to thoroughly test all Apple mobile devices that are intended to use their networks and test them in their intended environments that include using Macs with versions Apple deems necessary to properly fulfill new test products.

As for iOS 4.2, our source reports that it was actually due last Tuesday but a bug was found that did not display Japanese characters properly and forced Apple to fix it. The iOS 4.2 GM was supposed to be released on October 26th.