As most of you probably know by now, someone posted a similar thread on the Thunderbolt board and he or she is getting pretty lit up over there. The OP hasn't stepped forward with a link to prove were they read it or to defend themselves. I assume this is a hoax, but I can't say 100% for sure. I just wanted to mention it here so folks who haven't read the TB board won't flip out as soon as they see no more LTE devices until tiered data pricing. While that might ultimately be the case, I don't believe it is anywhere near official.
To answer this OP's question...I had the Thunderbolt for 9 days. I live in a strong 4G area near Clearwater, Florida. Only once did I notice 4G was not available. At the same time, neither was 3G. It lasted maybe a minute or two. But that only happened one time. 3 days after I purchased TB I traveled south to Naples, Florida which is a non-4G area. I didn't pay attention to when it switched to 3G, but when I got to Naples TB was in 3G mode and stayed that way the whole time I was there. No problems at all. I used the phone during my drive south (that is when I realized how AWFUL the speakerphone feature on the device is) and the phone operation worked except for the volume of the speaker. Again, I didn't check to see when 4G came back but it was seamless to me. I never had to reboot the device in the 9 days I had it.
Mostly, the device was brilliant. Except for that one glaring issue of the battery, and for me, the speaker. However, I sure wish Bionic had a kickstand. Somebody needs to make a case that has one just like TB's. I'd buy it