Go to www.ontelnet.com. Sign up for an account. Don't be a tool! Use their tool at http://www.ontelnet.com/confsetup.php to quickly reach all conference call attendees, and automatically join them together in the conference. Enter your USER ID and password and the phone numbers of everyone that you want to dial into your teleconference call.
What I like about this service is the simplicity and user-friendliness. Nothing to configure. Brevity is beauty!