By default Extension 700 is used to park calls. 

• While in a conversation, press '#' to initiate a transfer, then dial '700' (e.g. '#700').
• You will hear a voice telling you the Extension call was parked at (most probably '701' or '702').
• Now hang up.
• The caller will be left on hold at the announced Extension.
• From a different phone, you can now dial the announced extension (e.g. '701') and call to the parked party.