Direct-to-device satellite service lets an ordinary mobile phone connect straight to a satellite when no mobile tower is in range. It is also called satellite-to-phone service, or a non-terrestrial network (NTN). The best-known use today is satellite SOS: sending an emergency message from a place with no signal.
Earlier, a satellite phone was a special handset with a large antenna, and it cost much more than a normal phone. Direct-to-device service uses the phone you already have. The phone's own modem chip sends a signal to the satellite. For some services, this must be a recent chip built to support satellite signals. The satellite relays it to a ground station, which passes it to the mobile operator's network, through its packet core. From there, the message reaches its destination like any other message. On some services, the phone shows the operator's name as usual.
There are two approaches. The first uses existing geostationary satellites, about 36,000 km away. A phone's antenna is small and its transmitter is weak. So over that distance only a little data gets through: short text messages, not calls or video. The second approach launches new, large satellites in low orbit, a few hundred kilometres up. These are designed to act like mobile towers in space, and should later carry calls and data too. The difference between the two orbits is explained in LEO and GEO satellites. Both approaches are now live in some countries. For example, in the United States, T-Mobile has sent text messages to ordinary phones through SpaceX's low-orbit Starlink satellites since July 2025. Calls and full data over low-orbit satellites are still being developed, and some companies are still launching their satellites. In India, the government-owned operator BSNL announced a service of the first kind with Viasat in 2024, but it is not yet widely available on ordinary phones.
Say a trekker whose phone and mobile plan support satellite messaging crosses a high pass in Uttarakhand, two days' walk from the nearest tower. He twists his ankle badly, and his phone shows no network. He opens the phone's satellite messaging screen. The screen tells him to hold the phone up towards open sky, away from the cliff. He chooses a short message, "Injured, cannot walk", and the phone adds his location from GPS. The phone takes about 30 seconds to send it to the satellite. The message reaches the emergency contact he saved earlier. Later, a reply reaches his phone the same way.
The same idea serves machines. A cellular IoT module in a container tracker can switch to a satellite at sea, and send its location once an hour.
New satellites in low orbit add to the crowding of space, which space situational awareness (SSA) tracks. Ships and aircraft need far more data than one phone, so they use maritime and aviation satellite internet instead.