I just got off the phone with a 2nd tier tech myself. He, fortunately, is a Thunderbolt owner and is incredibly frustrated himself with the random reboots and dropped 3G connectivity. He would like me to convey that they have a high alert notice that has gone out to all reps on this, and that they just had a meeting regarding it. They are passing along all information to HTC and are attempting to put the pressure on HTC to put out a rapid fix. He says that, at this point, sending out replacement phones would not necessarily be the best option, since it is clearly a software issue, but agreed that this might be something they will have to do in the future. I suggested throwing in a free extended battery for everyone experiencing the problem, and then complained that the Droid Charge manages to cram in a 1750mah battery, so what the heck is HTC's problem?? He agreed with me, not that it really matters. Just thought that I would report....so if you are having this issue, please register it with Verizon.
Also, the Thunderbolt is not listed on the HTC website on their support page. I imagine it has an "original" name and became the Thunderbolt when it was sold by Verizon. What is this phone? The Desire?