From Verizon's Support page for the Thunderbolt:
http://support.verizonwireless.com/system_update/thunderbolt.html
Verizon Wireless is pleased to announce a new software update, Build Number: 2.11.605.9;
Baseband: 1.48.00.0930w_3, 0.01.78.0916w_3, for your ThunderBolt™ by HTC.
Verizon Wireless and HTC encourage you to download this update.
Device Features
+ Resolved issue with contact ringtones.
+ Improvements to notification volume.
+ Updated local streaming playback mechanism when network connection is not available.
Apps & Widgets
+ Updated Twitter API for Peep/FriendStream.
+ Clock app included in All App list.
+ Improvements in Exchange ActiveSync.
The size for this software upgrade is 36.152MB.