In Japan, mobile phones became ubiquitous years before the phenomenon spread worldwide. In Japanese, mobile phones are called keitai denwa (携帯電話), literally "portable telephones," and are often known simply as keitai (携帯).

A mobile phone is a portable telephone that can make and receive calls over a radio frequency link while the user is moving within a telephone service area, as opposed to a fixed-location phone. The radio frequency link establishes a connection to the switching systems of a mobile phone operator, which provides access to the public switched telephone network (PSTN). Modern mobile telephone services use a cellular network architecture, and therefore mobile telephones are called cellphones in North America. In addition to telephony, digital mobile phones support a variety of other services, such as text messaging, multimedia messaging, email, Internet access, short-range wireless communications, satellite access, business applications, payments, multimedia playback and streaming, digital photography, and video games. Mobile phones offering only basic capabilities are known as feature phones ; mobile phones that offer greatly advanced computing capabilities are referred to as smartphones.