Surprisingly, yes the same exact issue, it was my mothers Evo 4g. No matter what I tried I couldn't get it to connect back to the 3g network. The weird thing was that when I checked the data status(##33284#) it listed no errors and even said It was getting a EvDo Rev A IP address, which I wasn't expecting.
Restarting the phone didn't help, I ended up unchecking the mobile networks and then powering off the phone for a min or two. Then restarted the phone back up, and turned back on the mobile network and it reconnected.
But yeah, it was the same thing, she uses her wifi at the house, she left for work and realized at her job that she had no internet. Came back to her house and it signed back onto the wifi and worked fine. So I had her turn off the wifi on her phone to see if the 3g worked now and it didn't. So after troubleshooting the issue the one above ended up working. This just happened too btw, maybe a week ago. As far as I know it hasn't happened again yet.