I suppose that once we go to an AJAX-based interface, we could
accomodate that case fairly easily. However in the mean time, it is
going to be difficult to balance data flexibility with workflow. So
in order to avoid data management issues, I am going to suggest that
for the time being, we enforce a 1:1 relationship between contacts,
addresses, phone_numbers, addresses, and email_addresses. This should
cut down on bugs until we get to the point where we can remove this
(albeit arbitrary) restriction without interfering too much with
workflow.