You cant tether Kindle Fire to the phone via USB Cable, but you can tether a Kindle Fire to the phone via WI-FI(Mobile Hotspot). Refer this site for more info. http://technologizer.com/2011/09/28/kindle-fire-co
Hope this helps
Specifically, yes. Just activate the Hot Spot feature on your Epic and you can connect up to 5 WiFi Devices (including the Kindle Fire) to your Epic and share your internet connection.
To activate the Hot Spot feature you can contact Care or visit My Sprint. Just click the Manage This Device dropdown and choose Change my services. From there, check the Mobile Hot Spot feature.