My new mobile phone only stores 500 contacts on its memory and 200 on
the sim card (but you can only view one of the other). however i have
800 contacts, is there a way to expand the phone to cater for this?
for instance by somehow pointing the contacts memory to the expandable
memory stick (i have a 1gb one in there now which soudl compfortably
take it)?

If I understand exactly what you want I don't think there is a way -
you need to buy a phone with more storage.

You can check out
http://info-ninja.net/blog/2005/08/05/8-sony-ericsson-k750i-tips-and-hacks/

By all means don't close this question, some other researcher may have
better luck than I did and find your answer.

Good luck

Unfortunately there is no way and this is 100% solid.