I updated my iPhone 4 to iOS 4.2 last night and this morning found my AT&T voicemail being held hostage. My own fault, of course: I haven’t used my AT&T voicemail password in months. Fortunately, I found it and retrieved a (not very important) voicemail.
Other than that, no glitches with iOS 4.2 yet. As Computerworld noted, 4.2 for the iPhone is “nice, but not revolutionary.” It extends Find My iPhone availability to iPhone 4 owners without MobileMe accounts. (But note: For this helpful feature to work, you must activate it on the iPhone itself before you misplace the device. Here’s how.)