Siemens 600Series - Manual (Page 62)

3-4 ROLMphone 300/600 Series User Guide
Busy Standby Queuing
With Busy Standby Queuing, you can stay on a line until a busy
extension that you are trying to call becomes free. The busy tone
changes to music (or a ringing-beep tone), indicating that you are
queued. As soon as the extension becomes free, your call will be put
through automatically.
To standby queue
for an extension ➩ Listen for a busy tone.
➩ Stay on the line until you hear music (or a
ringing-beep tone). When the other party
hangs up, the communications server will
complete your call.
To cancel busy
standby queuing ➩ Hang up.