AD Contacts versus Public Folder Contacts

My company (management department secondary school) has asked me to solve the following problem:

environment: Exchange 2007, OWA, Outlook 2007

the secretaries have made / keep up to date a contacts folder inside the public folders and people use that list (address book) to e-mail, phone or fax contacts outside our organization, this list can not be used in the same way using OWA

the IT department publishes (using AD) lists that contain the contacts inside the organization and these lists can be used by both Outlook and OWA users

the IT manager has asked for a solution that meets the following demands:

contains both contacts inside and outside the organization
can be accessed by both Outlook and OWA and have the same look and feel
must be the only list available
all necessary contact information must be available (phone, addres, postal code, phone numbers, etc...) and be easy to print
must be kept up to date by one department
the list must also be used to share calendars inside the organization

does anyone know a solution?
thanks in advance,
pippin