Hook flash

Hook flash or flash (known in the UK as "recall") is a button on a telephone that simulates quickly hanging up then picking up again (a quick off-hook/on-hook/off-hook cycle). This action can signal the telephone exchange to do something. A common use of hook flash is to switch to another incoming call with the call waiting service. Another use is to indicate a request for voice conferencing, for example, a user may use a procedure like the following to initiate three-way calling:

1. Pick up phone handset (causing the line to be off-hook).
2. Hear a dialtone
3. Dial the first number and greet the first party
4. Press the hook flash button (or quickly tap the on-hook sensor on the phone)
5. Hear a stutter dial tone (a series of beeps followed by another dialtone)
6. Dial the second number and greet the second party
7. Press the hook flash button again.