Iridium Orbits
Almost, but not quite. They can also move satellites to different orbital planes.
They just launched their 10 satellites into the one orbit which is in the worst shape ("orbital plane 6"): it already has a small gap, and no spares left. In this case, eight are supposed to stay there and will be spread out by boosting them out of their current lower orbit into the higher one at appropriate times. Two will be moved to the adjacent orbital plane 5.
In the end, I think eleven satellites each (plus spares) are supposed to go into each of the six orbits (planes), so with seven launches lifting chunks of 10, that wouldn't work if they could not move between orbits.