I've searched for this here and don't see it. I've set a custom, contact-specific ring tone before but don't recall how. It doesn't seem to be under the contact, which is where it should be.
Phone is a 2.x.
OK I found it:
Go to the Contact. Do not press Edit. Hit Menu. Hit Options. Select Ringtone. Set Ringtone.
Seems wacky that you don't edit the contact to change the ringtone.