when i first got my thunderbolt..it would constantly switch from 4g to 3g and have that lag for a few seconds..frustrated me to the point where i wanted to return it..but now after a few tricks and patience..im 100% happy! Not only does the phone stay on 4G.. the signal is very strong and the 4G Mobile Hotspot works perfectly and its faster than my home internet haha..Battery life is good too so over all ive had success with 4G!
cheers