We have a client who has several VIP contacts. They pay an extra rate to get 24/7 support if needed (with a very short SLA). This is done on a per contact basis.
Within "Contacts" under a "Client" there should be a way to easily see all "VIP" clients. Maybe they get bumped to the top of the list.
Currently our helpdesk has to reference an excel file to see who a VIP is when a call comes in after hours (to find out if it's billable at the after hours rate or not)