Actually I found the answer. When we migrated to exchange 2007 I had originally left the default address book in place which was homed on a public folder database in exchange 2003 and did not also have web-based distribution on the exchange 2007 CAS servers.
I created a new address book, homed on an exchange 2007 public folder database with the web-based distribution, but I did not update the mail stores to refer to the new address book. So I just changed all the mail stores to refer to the exchange 2007 address book and re-started my outlook, then I told it to download the address book again. This time it took longer and voila, all the new SMTP addresses were listed! weee!