Create Global Contacts Directory for Microsoft Exchange

Question

I have a requirement from one of our Clients where he wants to Create a Global Contacts Directory in Microsoft Exchange Server. Let, me explain this. Suppose, there is some Company say "X". And, it has some Employees. Each Employee will have his/her contacts in their mailing list. So, the Global Contacts Directory should consists of All the Contacts of these Employees. And it should Also Sync them. Is this feasible enough is what i want to know and if Yes, How?