The cellular telephone (or "cellphone") represent a paradigm shift in modern communication. As soon as they became affordable, they revolutionized communication. They allow for private, two-way communication via voice or text between any two locations on Earth in range of cell phone towers. While they are an excellent form of communication during day-to-day life, they are difficult to predict during an emergency as they can suffer from outages of infrastructure (power down, servers out, etc...) or saturation of use rendering them nearly useless for voice communications. Text, on the other hand, may remain useable during saturation due to is lower resource requirements.
All cellular telephones are UHF FM two-way radios with an output of no more than .5 watts operating in the 800 - 900 gigahertz bands. Cellphones depend on a radio repeaters located at cellular towers to pick up their signal and boost it through the system. Modern cellphones may have wireless broadband connections as well as voice communications. Most modern cellphones also have GPS chips in them.