The information has been posted previously; I did post in the AA DFW-LHR in F award, "AA cancelled our seat assignments 2 days before flight", but will re-post here so it is easier to search (and find) in the future.
The OSO / Off-Schedule Operations desk at =1.800.446.7834 is open ONLY when there are weather or other conditions that affect large numbers of passengers. It is available to any / all whose flights are disrupted or at risk of being disrupted - basically for customers needing immediate assistance. They have quite a bit of power to arrange reaccommodation at these times -
more than EXP and Angels. Though the original article states the "desks will now be available at all of the carrier's domestic locations" it's really a virtual, tollfree presence.
Older FT thread discussing OSO thread.
Originally Posted by AIRLINE INDUSTRY INFORMATION-(C)1997-2003 M2 COMMUNICATIONS LTD
American Airlines has launched a special reservations desk providing options for customers affected by bad weather or other major delays.
The special desk - Off-Schedule Operations (OSO) - allows customers at the airport to call a special toll-free number to reschedule their travel without standing in line. <redacted incorrect information>
The OSO support (desk is) activated only when needed.