Editing Local exchange carrier (section)

==Residential local exchange services==
The following information applied to residential [[local telephone service]] in the Detroit, Michigan area during the 1970s and 1980s. Much about this subject has changed dramatically since that time, and continues to do so.

A local exchange carrier is a carrier of telephone calls and other communication services carried by telephone lines.  A local exchange is generally either an exchange within one's own LATA or in an immediately adjacent LATA. A call that is neither local nor long-distance is called a local toll call. A local exchange carrier normally sells package deals that include local and local toll calls. Local calls are customarily billed in by the call, or in blocks of calls. Residential local exchange carrier services typically charges <math>m+0.5p(q+|q-n|)</math>, where <math>m</math> is the monthly minimum and covers the first <math>n</math> calls, <math>p</math> is the price per local call, and <math>q</math> is the total quantity of calls consumed. Local toll calls are each billed at <math>m+(t-1)p</math>, where <math>m</math> is minimum charge for a local toll call, <math>p</math> is the per-minute charge, and <math>t</math> is the duration of the call in minutes. Local toll calls are traditionally grouped into two price ranges, called "near zone" and "far zone", with values of <math>m</math> and <math>p</math> higher for far zone.