At one time, I had set up my Yahoo! address book to synchronize with my Blackberry, so that my contacts in my Berry address book were coming straight from the Yahoo list. Now I cannot remember how I did it, in order to manually order a sync as I have altered some contacts in the list.
To the best of my recollection, it did not depend on having the Y! IM or mail clients installed (and I do not have them installed now). I could be wrong however.