Iridium is a military grade network, used by both the Canadian and US armies. The Iridium network consists of 66 Low Earth Orbiting satellites (to compare, GlobalStar has 18 satellites, Inmarsat has 3, Thuraya has 2). The Iridium network is considered to be 98% reliable.
In a car: Yes, at slower speeds, with a complimentary auxiliary antenna kit. At sea: Yes, best if used on deck, away from the vessels navigation equipment to minimize interference. In flight: Yes, with a complimentary auxiliary antenna kit. In a building: Not without an antenna kit. Subject to availability.