Interestingly enough, I've received this phone call 4 or 5 times in my life - always from AA. Up to a week in advance of a flight, and *usually* asking me to switch to one flight later at night out of Chicago to either LHR or CDG. Small voucher offer...maybe $200 to bump my itin back by 2 hours. It's clear that they aren't desperate, but at least they recognize an opportunity to shift people around a bit in advance and minimize the need for more expensive VDB/IDB at the gate.

I'm surprised they haven't coded this functionality into their app yet.