ZapBarge( )
Barges in on (monitors) a Zap channel
ZapBarge([channel])
Barges in on a specified Zap channel, or prompts if one is not specified. The people on the channel won't be able to hear you and will have no indication that their call is being monitored.
If channel is not specified, you will be prompted for the channel number. Enter 4# for Zap/4, for example.
Returns -1 when the caller hangs up and is independent of the state of the channel being monitored.
exten => 123,1,ZapBarge(Zap/2)
exten => 123,2,Hangup( )