We can start with an idea that needs no additional technology. Many people and companies operate Wi-Fi access points. Each of these points—whether used by apartment roommates, Starbucks patrons, or cell subscribers who get Wi-Fi “off-load” from their service providers—is connected to the Internet and often remains so even if cellular voice and data towers are out or overloaded.

via Outage after Marathon Bombings Prompts Emergency Network Proposal | MIT Technology Review.