As some of the more useful replies pointed out I was hoping for a recommendation from someone who had some headphones and could confirm they worked properly.
The HPM-90s are listed as fitting walkman phones. I used to have a walkman phone and the fitting was non-standard with two prongs.
On the SE site those headphones are displayed with the walkman fitting and not listed as working with the X10.
Sony Ericsson - Products - Accessories - Compatiblephones - HPM-90
So I'd be greatful to hear if someone actually has the HPM-90s and could say whether the fitting works with the x10 and also whether the screen display works?
The sony site does list the MH700s for the X10 but they look pretty basic and don't have specific music control functions...again if anyone has them, it would be nice to hear about it.