In the airline I work for it has always been included in post flight duties to call Crewing to check for changes. Most Pilots I talk to would rather find out what changes they have in advance to stand half a chance of planning their lives during a busy summer season.
How any airline can run without the 'call crewing after flight' or 'swipe system' is beyond me. I can assure you that the method of ringing in after a flight is a very effective way for Crewing to manage roster changes and reduce roster disruption. It's not an aid to 'shaft' people as stated in the first post that's a ridiculous comment. Trust me I like nothing more than to sit there all month and let the rosters run as published and keep everyone happy but in our airline we have delays, sickness etc so that's never going to happen.
Here's an example of how that quick call can save disruption;
Captain 'A' gets back from his flight and turns his mobile phone off. He has a change in two days time after his days off. He was on an 0600z standby but has been changed to a 1500z DLM flight. Crewing print off a list of all pilots who have changes for the following day and realise that Captain 'A' (knowing him well!) won't switch his phone on until 0600z at the start of his standby. 1500z DLM ! Ouch that won't be legal off his standby ,what shall I do? Damn he was our last standby aswell. I know we'll delay Captain 'B' off his 1130z PMI flight onto the 1500z DLM and call captain 'A' for the PMI which is legal. Oh and sorry Captain 'A' you'll now be doing Captain 'B's 0630z PFO tomorrow as he won't be in hours. He'll be doing your 1300z SZG instead.