1. When in a call, tap on the Add a new call button.
2. In the Add a new call window which opens, search for a person you want to add to the call.
3. The app finds the contact.
4. Call the selected contact. Please note that the first person is put on hold in the meantime.
5. When the selected contact picks up the call, click on Merge to create an ad-hoc conference.
6. You are now in an ad-hoc conference.