agn@c

how would one go about designing say
an employee.aspx that has fields say 1)employee id textbox 2)employee name textbox 3)employee Phone# textbox
with mandatory validations for all 3 fields and this is to be used for a business unit say A of a company. This page would have a save button and would make calls to a component say Employee that has a method say SaveEmployee(int empid,string empname,int empno).

Now down the line Business unit B of the same company needs to use the same page but will add one more field say employee mobile no,let us assume that
in addition to name and id only one of the phone numbers is mandatory ,also keep in mind when a user of business unit a logs in hes should see only emp id,emp name ,emp phone # fileds but a user of business unit b will see
emp id,emp name ,emp phone # and emp mobile # fields.

What i am really asking is how should i approach my desgin when i am designing an application for business unit A of a company and down the line business unit b will start using the same application and will present its requirements at that point of time say add some fields to an existing module as well as some business validations or they might remove some validations or mix and match etc..

Thanks,
agn