Outlook 2010
If you have recently upgraded to Outlook 2010, the location of your toolbar is in a different location.
Check the Add-Ins tab in Outlook.
Outlook 2007
Your toolbar may be disabled
Check the following location. (Disabled Items)
If the toolbar has become disabled it will appear on the list below.
Telephony Toolbar Call Control
Telephony Toolbar Services
Highlight the toolbar, Click Enable and Close.
You should then exit Outlook, pause for 30 seconds and restart Outlook.
You toolbar will now be available.