Alright, sorry about that, I fell asleep last night prior to testing this. I tested the short 2-3" Belkin iPod adapter that was linked before, as well as the longer Philips
adapter with a mic that I mentioned, and my own Meelectronics headphones with in-line mic/button. They all worked exactly the same despite the fact that the first one doesn't have a microphone, the electric signal they all send thru the third marking on the 3.5mm jack is the same after all.
On a stock EVO 3D, one press of the button on any of them will start the music player (with the phone locked or oherwise), and a second press will obviously pause it. A double click or press will dial your last dialed number, and pressing and holding will invoke voice search just like long pressing the search button. Pressing the button while the phone rings answers the call as expected and pressing it again hangs up. There's no triple press functionality and the volume buttons on the Belkin thing did nothing at all.
With Headset Button Controller installed you can change any of that behavior, and assign functions to triple press, amongst a lot of other things... And it integrates just fine with the stock player, so if you want more control over your button functions, it's probably worth the $2.60-ish. If anyone wants it tested with any other app just lemme know, tho HBC probably covers the expanded needs of most even if your particular player doesn't.
HBC also has support for what it calls left and right buttons but these definitely don't correspond with the volume buttons on a standard iPod adapter, not sure what headsets have 3 buttons which HBC might recognize... That Kplisch set mentioned before might be one.