The Nokia Lumia 820 for AT&T is now receiving the 1232.5962.1314.0001 software update which brings improved automatic display brightness adjustment, Fix for screen blanking during a call, Fix for connectivity issues in certain network conditions and a couple performance and stability improvements.You can check for the update availability by heading to Settings > phone update on your device and click Check for Updates. If the update is available you can install it on your device OTA (over-the-air)
The 1134 update for the Nokia Lumia 820 has the following new features and improvements:
- Improved automatic display brightness adjustment
- Fix for intermittent screen blanking during a call
- Improvements for connectivity issues in certain network conditions
- Performance and stability improvements
source - Nokia