In early August 2011, Iridium 11 (originally 25577, 1998-074A, but currently labelled by Space-Track as 25578, 1998-074B), which had apparently taken over from Iridium 23 (24906, 1997-043D) in November 2010, was moved around the plane, evidently to take over from Iridium 26 (24903, 1997-043A).
This suggests that Iridium 26 must have failed on station, and also that Iridium 23 retained some functionality.
Orbital Plane 2 has no other spare satellite.