Now that we all know how easy it is to flash a .zip, there's very little we can't do on our HTC EVO 4G. Using that simple method, we can now flash custom ROMs, install apps and tweaks that aren't available as .apk files, apply themes, and even update all of the phones radios without waiting for HTC/Sprint to release them officially. There are other ways to do some of these things too, but flashing a .zip via recovery mode is probably the most common.
If updating the radios piques your interest, then you'll be glad that Calkulin is part of the xda-developers forum because he's posted links to the latest versions of all the EVO's radios (baseband, WiMAX, PRI, and NV). He's got all the previous versions there too in case you need them.
Note that flashing the WiMAX, PRI, and NV radios requires S-OFF, which anyone who rooted with unrevoked 3.21 already has. Oh, and don't flash any of the updates if your radios are already up-to-date, as doing so can sometimes cause problems.
You can check your current baseband and PRI version in Menu -> Settings -> About phone -> Software information. I don't know how to check the NV version but your WiMAX version can be viewed by using a terminal emulator (such as Android Terminal Emulator, one of G&E's top 10 root apps) and typing in the following commands, hitting enter at each line break.
See this guide from SteelH for more information about checking your current WiMAX version.
Warning: Some people have reported reduced data speeds and non-functional 4G after flashing these updates, so update at your own risk. Updating the PRL and profile (Menu -> Settings -> System Updates) has fixed the 4G problem for some, and others recommend flashing each radio separately instead of using the combo pack.
For what it's worth, I have the latest baseband, PRI, and WiMAX versions (I don't know about my NV version, so I didn't flash the update) on my rooted EVO, and everything works as it should.[xda-developers] Thanks, Chris!