Call Waiting is a phone feature that allows you to receive incoming calls when you are already participating in a call. In its typical implementation, a beep informs you that there is another call being made to your number. This beep will occur in place of rings. This writeup will address the function and use of call waiting in the United States of America, as the behavior varies worldwide.
In order to pick up the call, you initiate a partial hangup called a flash, by depressing the hook switch (the switch, typically represented as a button or a pair of buttons, which causes the phone to hang up when returned to the cradle) for around a half second. I believe the minimum duration of a flash is specified at 150ms. Newer-design phones, or simply newer phones typically have a flash button which initiates a flash for you.
Performing a flash when a call is coming in on call waiting allows you to answer the new call, and flashing allows you to switch between the calls until one caller hangs up. In some systems, hanging up the phone while you have someone on hold will cause the phone to ring until you pick it up, or they hang up; hanging up the phone again will disconnect the remote caller. In other systems, hanging up the phone disconnects any callers, on hold or otherwise.
In the past, call waiting was more or less guaranteed to terminate a dialup modem connection, but current error correction techniques in modems prevent this from happening. You can change the modem's timeout parameter to a lower value on modern modems to make them less resistant to the call waiting signal, if you want call waiting to disconnect you from the internet so you can take a call. A phone hung up while a call is incoming from call waiting will begin ringing.
If you don't want to be disconnected, the most effective means is to utilize the call waiting cancel code, which is typically *69. In some areas, it may be *67, *68, *71, or even other numbers. Commonly, a whole range of codes are found together in order to enable or disable special features, like Caller ID blocking. A pause is necessary between the star code and the phone number; when we are constructing dialing strings for modems, we use a comma (,) between the code and the phone number to get this pause. Some modems (such as even some earlier models from US Robotics) also can use the letter W in place of a comma, meaning wait for dial tone. This is also commonly used when automating calling card calls, although most of them now use voice prompts exclusively.
Call Waiting is similar to another feature commonly known as Three-Way Calling, the difference being that Call Waiting only allows you to receive incoming calls, while three-way calling only allows you to make outgoing calls when you are already on a phone call. In spite of this consuming no more resources than call waiting, and in fact being based on the same phone switch functionality, it is sold as a separate feature.
Cellular telephones frequently also support call waiting. This is generally a standard feature of any current cellular telephone and system. The behavior of call waiting varies from phone to phone; some phones provide not only this functionality, but also the three-way calling. Typically, cellphone call waiting allows you not only to answer the calls separately, but also to tie them together into a three way conference call. The means of answering a call waiting call vary from phone to phone, but typically speaking instructions are printed on the phone's display when a call comes in. For Motorola Triplets phones, which includes both my Motorola V300 and V555, this is the right "soft key" (a key that is unlabeled, whose function shifts, and whose current function is displayed on the status bar at the bottom of the screen.)
If you have any information on how call waiting functions in other countries, please /msg drinkypoo.
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