Indeed in our forums, AndreiX confirms that his firmware has been updated to version 20105 , up from the earlier 20100 for a few users recently.

We’ve received a few tips today that some users of the international, unlocked HTC 8X are receiving a notification for an over-the-air update for the firmware.

Unfortunately, we don’t have enough information at this time to state how widespread this update is, if it’s for carrier branded devices or what it even does (HTC is a lot less forthcoming on these updates than a certain other company).

Update: At least for Verizon users, you are evidently getting this update too and it fixes three items (thanks, aceoforder):

Fixes the "SIM CARD NOT DETECTED" error

Fixes an issue with Skype calls not having audio

A battery-drain bug that can occur when a user enables Internet Sharing and then turns it off

If you get the update and vouch for any changes, please share your experience (and region/carrier) in comments for others!

Thanks, Casey M., zikifer, and JellymanEN, for the tips!