this happened to me last night. all of a sudden my Mobile network was offline all by itself. playing around with it i figured it out. long press the button on top of the phone and at the bottom of the menu is a "mobile network" button (below the airplane mode). it was just off in my case.

 

This happens to me too but I don't have great data coverage in my house. Keep in mind that phone and data is two different signals. Meaning that just because you have decent bars doesn't mean your data is going to have good connection. This is what's going on with me. I've talked to advanced tech support several times.

 

Hi,

I'm in the same boat. When I have time this weekend I'm going back to a clean stock rom.

I went in to Verzion today and saw that a droid had stable 3G.

http://androidforums.com/evo-4g-support-troubleshooting/271951-evo-verizon-3g-data.html

 

Update:

I've now wiped the phone and I get no 3G data with it seems the same setup.