An internal AT&T email, discovered by WPCentral, revealed that the update will roll out to Lumia 900 handsets on Jan. 30.
Microsoft previously confirmed that the update should start to arrive by the end of the month, so the Lumia 900 update is squeaking by just ahead of month's end.
An unofficial Windows 7.8 update for Lumia 900 devices leaked online last month, though the download came with the risk of wiping a user's data from their handset.
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An update worth waiting for
Windows 7.8 provides mostly cosmetic upgrades with customizable sizes and color themes for live tiles that make the legacy smartphones at least look like it is running Windows Phone 8.
The update also adds the Bing image of the day as a wallpaper option for the lock screen and improved security features, along with some behind-the-scenes API improvements.
So far only the Lumia 900 is confirmed to receive a Windows 7.8 update on Jan. 30, with no word from AT&T regarding other Windows Phone handsets.
Updates generally take a few weeks to roll out to all handsets, so there is a good chance the update time frame could run as late as mid-February to reach everyone. The good news though is that the long wait for Windows Phone 7.8 is finally, slowly, coming to an end.