When adding a contact to the person record, or editing a contact that currently exists
 

If the contact already exists for the person, display message, Error: Contact: Already exists for the person.  

Criteria to match will be contact type, contact subtype and detail.        

CND51

BR88

When adding a contact number of the same type
 

The added contact number will become the current contact number and the previous number will remain as history in the contact tab.
 

CND52

BR89