Search in contacts is limited to first name / last name and possibly nickname (when list configured by nickname).
A way to search the other fields.

https://maemo.org/community/brainsto...on_all_fields/
or
http://maemo.org/community/brainstor...on_all_fields/

I strongly favour solution #1 (KISS, ctrl-f for a full-text search)

(Edited to add http link for people not logged in into maemo.org)