Nokia and Microsoft have pushed out an over-the-air (OTA) update to AT&T Lumia 920s and 820s. The new update is a pretty important OTA update, with the companies saying that it will help Bluetooth reliability and connectivity, bolster Nokia Messaging, improve start-up performance, and update battery management.
Currently, you'll have to be on AT&T or Canadian's Rogers to get the update, though Nokia insists that they are "working with our operator partners in all regions to ensure the highest quality experience in every market." They add that they are "working closely with Microsoft...to deliver these updates to other markets in early February 2013."
So, if you have a Lumia 920 or 820 on another carrier, you have another 2 months, or so, to wait until you get these same improvements. Of course, you're highly encouraged to download the OTA update if you can as the fixes and updates are pretty significant.