On Motorola's, you can disable the VCast Browser Popup by right clicking the M task bar and selecting the option to 'do nothing'. However, you can't do that with the HTC Thunderbolt.
How can I disable the VCast Browser popup on a HTC Thunderbolt?
Below I have provided some instructions from your owner’s manual that might help you to chance the setting for the VCast browser popup. You can also click on the link to be directed to the owner’s manual on our My Verizon web site.
Connecting your phone to a computer
Whenever you connect your phone to a computer using the USB cable, the Connect to PC screen opens and lets you choose the type of USB connection. Select one of the following choices, and then tap Done:
Select this option if you only want to charge the battery while your phone is connected to your computer.
Select this option to synchronize contacts, calendar, and other information between your computer and your phone. For more information, see “Synchronizing with your computer” in the Accounts and sync chapter.
This mode is available only when there’s a microSD card on your phone. Select this mode when you want to copy files between your phone’s storage card and your computer. For more information, see “Copying files to or from the storage card” in this chapter.
When Disk drive mode is enabled while your phone is connected to the computer, you will not be able to use apps on your phone to access the storage card.
Internet Connection Mode
When you do not have Internet connection on your computer, you can select this mode to share your phone’s mobile data connection with your computer. For more information, see “Using your phone as a modem (tethering)” in the Internet connections chapter.
If you don’t have a data plan for your phone or you don’t have access to a Wi-Fi network, you can select this mode to share your computer’s Internet connection with your phone. For more information, see the Internet connections chapter.
Setting your phone’s search options
From the Home screen, press SEARCH .
When the search box appears, press MENU, and then tap Settings.
Tap any of the following:
Web search engine
Choose a web search service you want to use.
Select areas to search
Choose the types of items or apps to include in the search. You can also press and hold and arrange items according to search priority.
Even with the phone set to charge only it still has the popup.
Go into your autoplay settings and set it to do nothing when your thunderbolt is plugged in. It doesn't matter what that is set to as when you select one of the options they all still work. Just you won't get the initial popup.