The problem
Someone calls for a person who is not in the room. The options are to shout, to carry the phone, or to take a message — and taking a message is how a call for one person becomes an errand for another.
Mobiles do not solve this at all. A call on your phone is on your phone; the only handoff is putting it on speaker and walking.
What parking does
Answer in the kitchen. Dial 700. The call is parked and you are told the slot number. Walk away.
The person it was for dials that slot from any handset in the house and picks the call up where they are. If nobody collects it, it rings back rather than being quietly lost.
Why this feels like a real phone system
Because it is one. Parking is a standard PBX feature that every office had, and it maps onto a house perfectly — the same problem exists, just with fewer desks.
It is the feature that makes people realise the house has a switchboard rather than a set of extensions.
Details worth knowing
Parked calls hear hold music, so the caller knows the line is alive. Silence is indistinguishable from a dropped call.
Timeouts ring back. A forgotten parked call returns to the phone that parked it rather than sitting there forever.
Slots are announced. You do not have to remember a number; Asterisk tells you which one it used.