Kids Web Japan

Mobile phones work by sending and receiving wireless radio signals. The handsets that people carry with them communicate with each other via base stations that are interconnected by way of switching centers. Base stations are located every few kilometers throughout the country, and mobile phones can be used just about anywhere that has a sizable population.

There are four brands of mobile-phone service in Japan at present: i-mode (operated by NTT DoCoMo), au (by KDDI), Vodafone, and TU-KA. Behind the spread of mobile phones in Japan lies the competition between these different service providers, which have worked to set up networks of base stations, bring down costs to the user, and make their phones easy to use.

Lithium-ion batteries (NTT DoCoMo)

In the early 1990s, Sony Corp. developed lithium-ion batteries that were light, thin, and capable of storing a large amount of power, and other major makers rushed to keep pace. As these new powerful batteries became commonly used, mobile phones became small and light enough that a user could comfortably fit one in his or her pocket. The spread of mobile phones has been spurred by technology developed in Japan.