Satellite phones

In times of disaster and war, satellite phones are very useful if land-based communications infrastructure is destroyed. This American technician is communicating with a US hospital ship via satellite phone in Nias, Indonesia.
Source: Wikipedia

Satellite phones are mobile phones that communicate directly with communications satellites in orbit to make and receive telephone calls. Depending on how the satellite system is built, the coverage may include the entire planet or only specific areas.

Because satellite phones do not rely on ground-based transmitters, they are very useful in remote areas where it is not possible to build and maintain land-based phone networks. In times of disaster and war, satellite phones are very useful if land-based communications infrastructure is destroyed.

Satellite phones have not yet become widely popular due to their bulky size and relatively high cost per call. However, the cost and size of satellite phones continues to decrease as technology progresses and one day they might become a common communications tool.