multi-user, user based calendar

I run a wordpress website designed to service an internal sales force working from home. One critical area of functionality we would like to add is a user-based calendar where sales reps can schedule events (like call-backs, reminders… same sort of stuff you’d see in Outlook). So each user would only see their own calendar. Admin would have access to either one gigantic calendar where they see everything that’s going on, or each sales reps’ individual calendar (so that managers can ensure that everyone is working). If this could also include sales-based tools (like storing contact information, etc… that would be a huge plus. I guess what I am asking is, is there a plugin that is meant for sales-reps working from home like this? If not, is anyone interested in building it?