I am sorry that you are having problems. Have you tried any steps yourself to fix it such as remove/replace battery or turning on airplane mode and then turning it back off? Or you could also try a reset if you have already tried these things...it would be a last option of course because you don't want to lose any of your information. Anyway, if you are still having problems after these steps, please reply here or private message me. Thank you!
Unfortunately, I've done all the recommended techniques of trying to turn the 3g network back on, and nothing has worked. I did go to sprint and used my rebate to buy an iphone for my sister. They had to switch my number to the iphone, then put it back on my evo, but they said nothing would change. Would that have anything to do with what I am experiencing?
It's possible that using your line to upgrade to an iPhone would cause problems connecting to 3G. Anytime the active device on a line changes, the 3G 'password' is reset and must be updated. This is done by updating profile via Menu > Settings > System updates > Update profile. Let me know what happens.