I definitily agree with this, but as an FYI I wouldn't mind an adapter (with mic and button) to allow full functionality using existing headphones.I'm having a hard time understanding why people are obsessing over the headphone jack. Sure, it would be nice if my horribly expensive Shure headphones worked without modification with my iPhone... but hey, when Shure or some other high-end maker of headphones comes out with a set specifically for the iPhone (with the mic included for phone calls) I'll have to buy them anyway. I honestly don't want to use my Shures with my iPhone because I can't take a call with them in.
Face it, for your headphones to be fully functional you'll need to upgrade your headsets. It's a fact of life, this is a totally new product, not 'just another iPod'.
These things are very cheap for the Treo. In case I'm not making myself clear, here's one for $6, shipped (for Treo!):