Serval

Communicate anywhere, any time ... without infrastructure, without mobile towers, without satellites, without wifi hotspots, and without carriers. Use existing off-the-shelf mobile cell phone handsets.

Serval enables mobile communications no matter what your circumstance: mobile communications in the face of disaster, in the face of poverty, in the face of isolation, in the face of civil unrest, or in the face of network black-spots. In short, Serval provides resilient mobile communications for all people.

This system is the only mesh mobile telephony system that works on ordinary handsets, and is open source. It lets you use existing telephone numbers and can work without needing an internet connection.