The Windows Phone 8 GDR2 software update has reportedly started reolling out to HTC 8X devices on the AT&T network starting Thursday. The update which is being offered over-the-air (OTA) is around 207MB in size and brings the 8.0.10327.77 software version.The GDR2 update brings support for LTE bands 2 and 5 along with enabling the FM radio on your Windows Phone 8 device. You will have to plugin your earphones in order to make use of the FM radio. You
You also get access to the Data Sense application which keeps track of your monthly data usage. You can monitor how many days remain on your billing cycle and even find out which apps are consuming the most of your monthly allowance.
Other new features include Sync support for Google Contacts (CardDav) and Google Calendar (CalDav) along with additional enhancements to Bluetooth, music and battery performance.
AT&T refers to the GDR2 update as a staggered at the begining which means that it maybe a few days before it reaches out to all devices. If you have set updates to download automatically you should receive a notification once the update is ready to be installed on your device. You can also manually check for the update availability by heading to Settings > Phone Update > Check for Updates.
source - AT&T