The services provided by professionals in particular field. For example, a company may charge a certain sum of money for the certain tasks their consultant accomplished for the company who ordered the service.
Feature allows subscribers calling to a certain number in order to connect to a conference call. The one, who dials the number, will connect to the conference. However as a conference controller one should give that certain number to all the participants and set the time for conference in order for the participants to be able to set up a successful conference.