How to give someone access to your Contacts (Outlook 2010)

• Click the Contacts button in the Navigation Pane if necessary
• In the Share section of the toolbar/ribbon, click 'Share Contacts'.
• Like sending an email, enter the name of the person to whom you want to grant sharing permission (click on 'To...' button to bring up Global Address List).
• Select the required permissions and optionally add a message for the recipient, click 'Send'.
  

Opening another person's Contacts

Assuming that you have been given the appropriate permissions you will be able to view and work with another person’s Contacts.

• Click on the Contacts button in the Navigator Pane if necessary.
• Click on the Open Shared Contacts link.
• Type the appropriate name or click on the Name… button to select that person from the Global Address List; then click OK.
  
• The other person’s Contacts folder is displayed in the Navigation Pane at the top. Click on each one as required to view its contents.