If you really want a headset, other than bluetooth, there is one on this page. I haven't tried it, I find simply using a standard headphone and the internal mic to work just fine. Some people say they just hold the speaker (d-pad) to their ear (axim upsidedown so mic is near their mouth) and that reduces or eliminates feedback, if you don't mind looking a little strange.
Opps, I just noticed this was in the X30 forum, so I guess what Gigi said is it.
Here is something that might work with the X30, specially if you want to listen to music while not talking on Skype, but it also uses bluetooth.
http://www.tekkeon.com/site/products-mytalker.php