No time was given but our bet is 9AM PT/12PM ET is when the update will begin to be available...

For those of you fawning over our sneak peek of the Lumia 920 OS and firmware update , you can go to bed happy tonight because tomorrow is your day. AT&T is now notifying employees internally that the combo OS and firmware update will be going live tomorrow, December 19th for both the Lumia 920 and 820 (no word on the HTC 8X, sorry).

The information comes via an internal AT&T email circulating around to employees that details the OS update, codenamed ‘Portico’ . The fix from Microsoft updates the OS to 10211 through a series of system patches, the main crux of which will fix a stability issue related to Bluetooth connectivity, causing isolated cases of OS resets or freezes. Portico will also deliver SMS call rejection, SMS mass delete and new firmware from Nokia that adds greater sharpening to the front and rear Pureview camera...

The email from AT&T states that

“The update will be processed over-the-air (OTA) via a Wi-Fi connection. This software update will improve the experience for a small number of customers who have reported issues with connectivity to Bluetooth devices, including times where an affected device appears to freeze.”

You may notice the pop up notification for an OS update tomorrow and you are given the choice to postpone the update until you are over Wi-Fi or at another time, but not indefinitely

“They have the option to select postpone or install the update immediately to their device. If the customer selects to "postpone" installation of the update, the notification pops up again in two days. The notification cannot be postponed permanently. Customers can also check the availability of the update from the Start screen by scrolling down to and tapping Settings > Phone Update > Check for Update. All customers will be notified of the update by January 7, 2013.”

T-Mobile and HTC are planning to update the 8X with a similar update starting tomorrow as well.

So far, the OS and firmware update have made our Lumia 920 even better than before. The update should also bring some fixes and enhancements for the Lumia 820, though we’re not sure what exactly those are. We do expect, however, to get a full details about the Nokia’s changes sometime tomorrow, so stay tuned to Windows Phone Central for all your Windows Phone needs!

Big thanks to Jeffrey, for the information!