It's not just Sprint phones. I think its Android in general. Im stilll running on Verizon on Droid X till the end of this month.
Almost monthly I need to wipe phone phone and reload. it starts with slow response on the Dialer Screen then Random reboots, lockups and just slow response. I grit my teeth , wipe the phone and spend the next hour reloading the apps back on and good to go for another month.
Just wiping cache doesn't do it either. have to do a total wipre and reload