rpose. A three-way caller dialing a sec- ond call almost certainly does not want spurious tones on the first call, so an extra step was added to the wireless three-way calling process. The first flash sends the call into a quiet mode so that the subscriber can send digits second call. 5 Once those digits are entered to the subscriber's satisfaction, SEND is pressed again, and the system attempts to complete the second call. From this point on, a wireless three-way call is the same as the landline version, with the SEND key be- ing used for a flash. Figure 16.6 shows a call-state diagram for wireless with call waiting and three-way calling. As in the landline case, the interaction between these two custom calling fea- tures can vary a little from system to system. The voice-mail service (sometimes called call messaging or call notes) provides the services of an answering machine, with the telephone network storing messages for the subscriber. It has an additional advantage in that if a new call comes in while you are on the line (and you do not have call waiting or have disabled it), the call will go to the automated answering service. This is not possible with a traditional landline answer- ing machine. Voice mail is available both on the PSTN and on cellular systems. The voice-mail system does not require any new states for the telephone itself, but one could create a state diagram to represent the system states. On the PSTN, the voice-mail service notifies the subscriber of new voice mail with a broken dial tone. The customer calls a special phone number to reach an automated message center and enters a passcode to listen to and to manage messages. On cellular systems, the network pages the cellular telephone over the signaling channel, and the telephone signals the user with a distinctive ring, a flashing light, a text message, or even all three. On some phones, the user can call the automated message center to listen to and manage messages using a single keystroke. A pass- code is not needed if the caller is 