Some people have different opinions on what a "hard reset" is:
In Sprint's eyes and hard reset is actually resetting the phone to the point where even you're phone number has to get reprogrammed into the phone (##786#). This will reset your phone back to factory settings and also reprovision your data and voice.
Factory reset will do everything a hard reset will do but does not reprovision your data or voice (your phone number never "left" the phone).