I'm having the same issues with my Moment, and I too am in an EVDO area.
My phone inexplicably enters Airplane Mode on it's own at least once a day, cutting off everything and then it won't come out of it until I restart the phone itself.
I notice that it happens more when I have PDANet going, but it also happens on it's own with little to no applications going.
*shrug* I'm hoping the 2.0/2.1 update that we're supposed to get will fix it.
- Sprint USA -