While it's not the big Android 4.3 update many are wanting, the HTC EVO 4G LTE also has an update pushing out today. The 3.17.651.4 update is a maintenance release, and the listed change log says HD voice will be enabled by default to go along with the requisite bug fixes and stability improvements to Sense.
This is yet another staged release, and not all users will see the update today. To see if you've got a seat on the OTA carousel, pop into the settings and check for a software update.
Source: Sprint. Thanks, @sanders_llc!