IPKall was a public switched telephone network to voice over IP call forwarding service. One way of doing call forwarding with ENUM is illustrated in the next figure. This type of fallback is a somewhat more complex form of call forwarding. All plans included call waiting, conference call and 1000 call forwarding minutes. Call forwarding is disabled by dialing *73. Call forwarding was invented by Ernest J. Bonanno. Secondary dial tones are often used in call queuing and call forwarding systems. In the DNS, NAPTR records are used for setting the subscriber call forwarding/termination preferences. Once someone answers, call forwarding is in effect. It resembles "busy/no-answer call forwarding".