Probable evolution of telephony

A statistical study for telephone development in various countries, based on normal development and occasional irregularities due to economic crises, wars and other events. It is found that the evolution of the telephone line density "d" follows the same pattern for many countries and may be expressed an a function of time: d = f(T + c), where "T" is time in years and "c" is a constant indicating the time lead or lag with respect to other countries. A mathematical approach is attempted. The actual development of the line density will probably follow more or less the logistic curve till a certain density is reached and will then gradually tend to a saturation density lower than the maximum given by the logistic curve. Subscriber sets per telephone line and telephone conversations are discussed briefly.