A satellite phone is a handset that connects to a satellite constellation rather than terrestrial cellular networks. The major networks: Iridium (low-earth-orbit, global including polar), Inmarsat (geostationary, global except polar), Globalstar (low-earth-orbit, regional coverage), Thuraya (geostationary, Europe/Africa/Asia/Australia). Used where terrestrial networks are absent (oceans, polar regions, remote terrain) or compromised (conflict zones, censorship environments, internet shutdowns).
What it means in practice
The choice of network determines coverage, hardware, and cost. Iridium covers the entire globe with no gaps; the handsets are smaller and the airtime is moderate. Inmarsat’s geostationary architecture leaves polar regions uncovered; the handsets work where the satellite is visible (line-of-sight to the equator from the operating location). Thuraya is the cost-effective option in its coverage area but useless elsewhere. Globalstar is regionally limited and less common in journalist and NGO kits. The encryption story is consistent across all networks: voice and SMS are not end-to-end encrypted by default, and the link emerges at a ground station that is subject to local lawful-intercept obligations. Treat the satphone like an internet connection of variable quality, with the same application-layer encryption discipline (Signal over data, encrypted email, VPN tunneling).
Who uses it, and against whom
Customer base: war correspondents, NGO field staff, polar and maritime expeditions, aviation cockpit and cabin communications, oil-and-gas remote operations, military and government deployments, search-and-rescue operations, expedition guides and remote-area travelers. The threat surface: in restricted countries, possession of a satellite phone may itself be illegal (Cuba, North Korea, Sri Lanka historically, several others; check before traveling). In conflict zones, the RF emissions can be direction-found by adversaries with the right equipment. In any jurisdiction, the link metadata is reachable to law enforcement on legal process at the ground station egress. The defenses are operational (minimize emission windows, use application-layer encryption for content) rather than at the network layer.
What you can change today
If your deployment plausibly needs a satphone, decide between Iridium (recommended for most journalism and NGO use; global coverage, smaller handsets) and Inmarsat (recommended where coverage permits and the bandwidth advantages of services like BGAN matter). Buy or rent the handset before deployment, activate the airtime plan, test the handset in varied environments. Carry a backup battery and a charging solution that works without grid electricity (12V car adapter, solar panel, hand-crank). For sensitive content: route everything through Signal over the data plan, never use native voice or SMS for material that matters, and treat every satphone session as an emission window minimization problem.