AT&T Merlin Legend MLX-10D User Manual page 185

Features
Camp-On
When you are transferring a call to a busy extension, you can
use Camp-On to keep the call at your co-worker's extension
for a longer period of time than Transfer allows. An
unanswered Camp-On call rings back at your phone after
30 seconds to 5 minutes, depending on how your system is
set up.
Camp-On is used in either of the following circumstances:
The extension receiving the transfer is busy. In this
case, the person at that extension hears a tone
indicating that another call is waiting.
The person is available, but does not want to take the
call immediately. In this case, the person does not
hear a tone when you use Camp-On.
NOTE:
You can use Camp-On only after you have started a
transfer, using one of the methods described in this
section. You cannot start a transfer with Camp-On.
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Transfer