Assigning Custom Form to Shared Calendar for All Users

We are using Outlook 2007 on an Enterprise Server.

I have a shared calendar for scheduling volunteers that many people
across the organization access. Due to situations where an employee
may need to contact a scheduled volunteer, I want to link the
appointments to their contacts. I know how to insert the contact item
into the appointment. However, I collect other personal information
on volunteers that I don't need everyone in the organization to see.
I want them to only have access to their phone number. Therefore, I
want to create a custom form that only displays that information. The
trick is figuring out how to set it up so when the employee clicks on
the contact item in the appointment, it opens to the custom form no
matter what user/employee clicks on it. Is there a way to make this
happen across the organization??

Thanks!