How do you use flash on a bell phone?

Question

me and my friend are trying to prank our other friend by going on flash, my friend has flash he also has bell and he doens't know how to use it

Answer 1

Switch Hook Flash Telecom Definition

A method of signaling a central office, key telephone system, or PBX by quickly depressing and releasing the switch hook on a telephone set, perhaps to answer another incoming call. Some Centrex and PBX telephone sets have special buttons that implement this function.

Switch hook - is that button used to hang up the telephone. Normally pressed when the handset is put back on phone.