According to MobileCrunch, the HTC EVO 4G OTA update that started yesterday morning soon after resulted in some users getting their EVO 4G bricked, jailbroken and stock versions. Sprint and HTC have temporarily halted the OTA update:
While the vast majority of consumers successfully downloaded and installed the most recent HTC EVO 4G software update, we have received a handful of reports from customers having some issues with the update. In light of this, HTC and Sprint have decided to temporarily halt distribution of this software release until we can investigate further. We expect to be able to resume software updates shortly.
Give Sprint a call (888-211-4727) and ask for a replacement and a credit to your phone bill for the month. You might also give your local Sprint store a try.