Repeat after me: HTC EVO premium data add-on is not just for 4G
I know a lot of people are unhappy about the mandatory $10 monthly premium data add-on that "comes with" the HTC EVO 4G, especially those living in areas without 4G coverage who feel ripped off, so I thought it would be useful to reiterate that the required charge is not just for 4G.
Sprint actually does a horrible job of explaining what the premium data fee is about (see below), but as others have previously noted and the screenshot above shows, the add-on gets you unlimited data (no 5GB cap) on both 3G and 4G.
The add-on isn't specifically for unlimited data, no, but it's not being enforced just for access to Sprint's 4G network either. By also paying for the Sprint Mobile Hotspot feature, you're actually getting the cheapest unlimited 3G/4G portable router around.
So don't feel bad if you're not in a 4G area; you're not really paying for something that you're not getting.