I tried Company Directory, and it worked for me. The procedure is a bit clunky, as you need to do the following in order to call a contact in the company directory:

1. Select Contacts
2. Select All Contacts menu
3. Select Import contacts
4. Select Import Mail for Exchange contacts
5. Enter name
6. Select Search
7. Select desired name
8. Select Import
9. Search the just imported name from all contacts
10. Select the just imported contact
11. Select the phone number you want to call

There are 11 steps and you have to search the name two times, first in the Company Directory and after you have imported the name, it has to be searched again from the phone contacts. The process could be streamlined, i.e if you import just one contact, after importing you should go directly to that contact's details, which would remove 2 steps.