Telephone Entertainment Line

Telephone Entertainment Line refers to a telephone number or numbers with (usually) an announce only answering machine, maintained for the purpose of providing entertainment over the telephone. These were most popular in Southern California in the 1960s and 1970s. Most lines played one short joke out of a pool that would rotate to a new joke each time the number was called, but others had a single long form (about three minute) comedy that would change every week or so. Still others were "comment lines" that were like a talk show on the telephone. The comment lines would either have a separate number for callers to leave their opinions on, or a single number that would accept incoming recordings on a given day of the week. Examples included New York Telephone's Dial-a-Joke Many of these recordings have been archived on the Internet.

...
Wikipedia