By "sub-form," do you mean the separate dialog with address details? That dialog is not customizable.

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Sue Mosher, Outlook MVP
Author of Configuring Microsoft Outlook 2003
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> I'm trying to add the field "Business Address PO Box" in the sub-form (or
> action button) "Business" in the contacts form and I can't find how to
> proceed. I know how to edit the "contact" form but not the sub-form. When I
> click on the "Business" button in the contact card, I get a new window
> entitled "Check Address" and that's the one where I would like to see the
> "Business Address PO Box" field. Anybody knows how to proceed?