My clients, colleagues, and friends rely on the fact that they can usually reach me in about ten seconds either by email or by dialing one globally-routable telephone number.
When computerized dialing systems were introduced, they replaced the need for manual telephone switchboards and, consequently, the switchboard operators that ran them.
When I botched telephone number selection during setup, however, I had to call Companion tech support for a code to access the dialing screen and the correct numbers.
Ask attendees who are not dialing in on a cell phone to place their cell phones on mute and keep them away from the telephone, as this can cause a loud buzzing noise.