This has to be a conspiracy of Apple and Microsoft to create compatible earbuds. iPhone has a recessed earphones port (see photo) and while it uses the plain 3.5 mm type, you'll have to use an adapter for many types of headphones. But not for Zune's headphones which can be plugged with no problem! ...
Anyway, I had a couple of no-name headphones that would fit in that port excpet for the Zune's :)
If you think about buying iPhone, check the list Engadget created with some compatible and incompatible earbuds .
Here is also a presentation on iLounge showing some of the available accessories for the iPhone.
[via PMPtoday ]