The HTC Evo was the first next-gen Android phone to receive the Froyo update. While early adopters were happy to get it, the Evo's version of Froyo wasn't quite perfect. Apparently, HTC had to cut some corners to get it out ahead of the game. Some Evo owners have noticed issues with battery life, contacts, and processor sluggishness.
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As a result, Sprint is pushing an update that is supposed to fix all that. 3.26.651.6 will bring your Evo in line with other next-gen smartphones that pack 2.2. An OTA update will be hitting at some point in the near future, but you can go to your settings tab and scan for updates now if that isn't speedy enough.