Problem with phone list.

Hi all.

I've qot a problem I need to solve.  I'm sure it's pretty simple; I just can't 
seem to get it, so here goes...

I've got a table, actually a view that joins 3 tables, that contains a phone 
number, a unique id, and a call duration.

The phone number has duplicates in it but the unique id is unique.

I need to get a list of distinct phone numbers and the coorisponding largest 
call duration.

I've got the idea that this should be a self-join on phone number where 
a.id<>b.id, but I just can't seem to get the max duration.

Any hints would be much appreciated.

Mike.