On July 1, 1987, WFAN in New York launched a 24-hours-a-day sports talk format. As the station notes on its website, since its birth "dozens of stations have copied the all sports format, but none have achieved the success and the popularity of the FAN."
Dozens may be a serious under-count. At least one sports talk station can be found in every major radio market in the country. (For the record, I'm partial to The Ticket in Dallas-Fort Worth.)
-- Bob Davis