You could use Search in Outlook or Outlook integration:
Search in Outlook shows your Outlook contacts in the Zoiper contact list.
To enable Search in Outlook you need to open settings -> preferences -> go to Contacts -> Search and enable Search in Outlook. Default value for Outlook profile is outlook and the password should be empty, max chars to search =0. This will show your Outlook contacts in your Zoiper Contact list.
Outlook integration allows you to directly dial your contacts in outlook via Zoiper.
You need to enable the Outlook addon during the Zoiper installation.
Now please restart Zoiper and Outlook (if running) .
Open the addressbook and right-click on a conact. You will see "Dial wth Zoiper" in the context menu.
Click it and Zoiper will dial the contact. It will launch even if it is not running at the moment.