In late June, 2005, Iridium 98 (27451, 2002-031B) commenced manouvering.
In mid-June 2005, Iridium 98 was raised from the parking orbit (673 x 670km) to the engineering orbit (752 x 744km), and its orbital inclination increased, so that it drifted away from orbital plane 4.
The original intention may have been to drift Iridium 98 to orbital plane 5, which had been without a spare satellite since Iridium 86 (25528, 1998-066B) took the place of Iridium 16 (24841, 1997-030F) in the operational constellation in April 2005.
The rate of drift was such that it would take about a year for Iridium 98 to move from orbital plane 4 to orbital plane 5.
Subsequently, in mid-October 2005, Iridium 91 (27373, 2002-005B) began manouvering in a similar way from orbital plane 3. Iridium 98, which moved beyond orbital plane 5, continued to orbital plane 6, arriving in May 2007, while 27373 [subsequently relabelled as Iridium 90] moved to orbital plane 5, arriving in January 2008.