This delimma has been bugging me, too. Searching for a decent pair of earbuds with a 2.5mm jack was pointless. I went to Fry's and picked up this cool little adapter for $4.99:
http://www.cellet.com/catalog/produc...6935&cat=&page=
It works out pretty well considering the cost. I like the microphone and answer/end button as well. The sound is pretty good, as long as you're using ear buds and not the larger over-ear phones. Since the cable on the adapter is short, you'll have to hold your phone when using the hands-free feature, but it sounds pretty good for both parties when using it. The only connection issues I've had is when carrying the phone (at waist level or below) and listening to music - occasional crackle, but not too bad.
I would definitely recommend this solution to anyone seeking to use their existing phones.