Using version 14.0.4536.1000 of Outlook 2010 and I cannot seem to be able to call Contacts using the ‘Call’ button anymore.
The TAPI2 driver is still installed and working properly.
When I select a phone number on a contact and click the Call button, nothing happens – I.e. I do not get the ‘New Call’ dialog of Outlook 2007 that allowed you to see the number being called and start/end the call.

There are three steps:

  1. Add the following key  to the registry: HKEY_LOCAL_MACHINE\Software\Microsoft\Office\Outlook\Call Integration
  2. Add a dword-value: TAPIOVERRIDE    and set it to 1
  3. Restart Outlook.

In addition you can customize the ribbon to have the Call-button directly on first sight.

Just right click the start(contacts) ribbon and say Customize the ribbon. Add a new group to the Start(contacts) ribbon rename it (i used TAPI) and add the Call-Command to that group. A possible position for the new group is after the Delete group. Worked fine for me