Outlook email - how to not see fax numbers??

[mooseAndSquirrel]

In Outlook (the full, although maybe this is true for express as well) when I compose a new mail item and click "To" to select from my contact list/address book, entries like my sister show up twice, one is her email address and one is her business fax. I can't imagine why the designers thought this would be useful (especially since you can't tell one from the other). Is there a setting to tell it to stop this obnoxious behavior and just show email addresses in the pick list.