what is the purpose of a flash button on a phone
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 a 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: Pick up phone handset (causing the line to be off-hook). Hear a dialtone