The admin at the official Sprint Community forums has made a small, but good-to-know announcement about the Evo 4G and the software version numbering. Sprint says Evos sold in November will have a different software version number than previous units. New models will have a software number of 3.30.651.2, and older models will have 3.29.651.5. This is due to a parts difference, and both versions are fully able to get further updates. No idea what the new part is, but Sprint assures us it won't change the user experience.
If you buy an Evo this month, tap the menu button > Settings > About phone > Software information, and you can check your version number. [Sprint Community] Thanks, Edgar!