Call waiting (or catch phone in Japan), in telephony, is a feature on some telephone networks. If a calling party places a call to a called party which is otherwise engaged, and the called party has the call waiting feature enabled, the called party is able to suspend the current telephone call and switch to the new incoming call (typically, this is done by pushing the flash button), and can then negotiate with the new or the current caller an appropriate time to ring back.
Call waiting, then, alleviates the need to have more than one line for voice communications. Note that since the waiting call creates an audible (for example, a 440 Hz beep every ten seconds in North America), call waiting can cause dial-up Internet access connections to terminate, unless the modem supports the most recent V.92 modem standard. For this reason, call waiting is often disabled on shared voice/data telephone lines. In North America, the NANP uses *70 before a call to suspend call waiting for that call. A stuttered then regular dial tone confirms the de-activation.
Type II Caller ID also works with call waiting.
Call waiting was introduced to North America in the early 1970s when the first generation of electronic switch machines built by Western Electric,the number 1 ESS started to replace older mechanical equipment in the old Bell System local telephone companies,. At first, some smaller municipalities had it only on a specific phone exchange (e.g., phone customers in Trenton, Michigan initially had to have a phone number starting with 671 to have call waiting due fact 671 was at that time the only exchange in that area served by one of the new ESS switches), but as demand for it became more widespread, it eventually became available on all phone exchanges as the older equipment was phased out.