https://wiki.asterisk.org/wiki/display/AST/Call+Parking

In the previous lesson we looked at transferring a phone call to a user. Transferring works great if you know exactly where to redirect the call. In some organizations, employees do not sit near a dedicated phone. Some employees move around the office during the day.

In this case ,it may be better to park the phone call, locate the individual that the call is intended for, and then have that individual retrieve the parked call. Essentially this is allowing us to put a phone call on hold with the ability to pick the call back up at a different phone location. When the phone call is parked in Asterisk, a parking location is announced through the phone. Once known, any phone that dials that location will then pick the phone call up.