Every iPhone review I've read (and I've read a lot) has stated in no uncertain terms that Bluetooth only works with Apple's hands free headset. But after reading this tutorial, I decided to see what I could find. It turns out that Proximity can find, and lose, my iPhone.
I've only tried triggering a few simple AppleScripts, but it has potential. I've noticed that the iPhone never stops searching for devices (well, the spinner in Bluetooth settings never stops), and this may seriously reduce battery life, but I've gotten inconsistent results at best. Running scripts is nowhere near as useful as a true wireless sync, but it's a step in the right direction.
[robg adds: The linked blog entry contains some pretty useful scripts to run with Proximity.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20070710060250502