FullHDMI app brings comprehensive HDMI support to the HTC EVO 4G
Nevertheless, it was one of the first phones to feature an HDMI port, and it would be a waste not to make full use of it.
Sound will only be output if you are running the Sense ROMs, which don't support landscape view of the homescreen, but you can always download Launcher Pro. And you will need an El Cheapo HDMI-to-micro-HDMI converter ($3-$5 on Amazon).
Add this to the $2.99 price of the FullHDMI app, and you can be watching HD 720p movies, play Android games, and overall mirror the phone's display on your big screen TV for under ten bucks.