According to Verizon, the update will bring HTC Watch, showing video titles available for purchase or viewing. Also, Amber Alerts are now visible and the text messaging app has been improved. The Microphone now works with the HAC enabled and the update adds improvements to Yahoo and Microsoft Exchange Email Connectivity. The whole shebang weighs in at 19.3MB which is about as lightweight as these things go.
The OTA update takes 2 to 3 minutes to download and 3 to 4 minutes to install. During the installation process you won't be able to make or take calls. If you own the HTC ThunderBolt, this might be your last hurrah, so enjoy it while you can.
source: Verizon via AndroidCentral