Well, I haven't seen any threads on this topic so I thought I might post one in case it helps someone else out there.
Previously, some may recall that I had two Thunderbolts (one for me and one for hubbie). He dropped his a couple too many times and ended up cracking his screen. The cracked screen then degraded to the point where the phone stopped responding to touch screen input.
I ordered a new digitizer and frame and swapped phones with him. I took his dead phone and he took my rooted Thunderbolt which I set up for him the way his previous phone was set up since it was easy enough for me to do for him.
I repaired the broken Thunderbolt and for a couple days, the phone worked fine. I went through the pains of setting up the repaired phone (but it wasn't rooted yet because I hadn't gone through the rooting process on his phone prior to it breaking). I spent time rooting it, then not a half day later, the keyboard started acting flaky. The letters 'e' and 'r' stopped working. Obviously this was unacceptable, um, well, I'll be honest, I was actually looking for a good excuse to go buy something else new to play with too!
So I went out and bought a smaller screen phone - the HTC Incredible 4G which just came out about a week or so before I picked it up at full retail. (Yeah, the price we pay to keep our Unlimited Data Plans, right?) The DINC 4G has been a great phone, despite some of its limitations compared to the Thunderbolt. ICS took a little while to get used to but after I've had it for several weeks, I decided to disassemble the Thunderbolt and see if I could fix the touch screen issue. I figured, it wouldn't hurt to check all the spring contacts beneath the screen, to see if they're all touching properly.
When I took the unit apart, I could see that a couple of the spring mechanisms weren't pressing up against the under side of the mating connection, so I carefully stretched them out just enough to add some spring force back into them, then put everything back together.
Everything seemed to be working again so I went into the Verizon web site and re-activated the Thunderbolt using their online tool which only took a couple minutes, mainly because you have to remove the battery to get to the IMEI Number under the battery, and the SIM Card Number has to be available as the last step in the activation process. (None of this affects the Unlimited Data Plan by the way). Moments later, I powered the Thunderbolt back up and tested the alphabet. No issues at all!
If the problem returns, I'll update this post. I thought my experience might be useful to someone who is having similar problems. You may not need to replace your phone at all, if you're out of warranty and if you have an Unlimited Data Plan and your only option is to purchase a phone at full retail which is expensive for these advanced devices.
Thanks for reading!