I have a droid razr (and I'm pretty new to it so please have patience as this might be a "mia culpa" thing)...
If I go into a 4G area (e.g. I'm getting the idication of 4G coverage) I lose my data/internet access. Subsequent to this I cannot get 3G access (when I leave 4G, enter 3G only service) - in fact my 3G bars (indicator of signal strength) show a red circle with the red diagonal line through it. If I power off/on, all works correctly (I once again have 3G access in the 3G service area - well until I go into a 4G area where the above is repeated).
So (1) why can't I get 4G service to work and (2) why does 4G "pollute" (render inoperative) my 3G service on my razr?