Why do most Chicago radio stations have phone numbers starting with the 591 exchange (after the 312 area code)? What type of commercial scheme or conspiracy is at play?
312-591 is what is called a “choke exchange”. It’s a telephone exchange designed to handle a large volume of telephone calls. Radio stations, event ticket vendors, and other businesses that receive a large volume of local calls are usually serviced by a choke exchange.
Wikipedia has a list of several choke exchanges in the US. You’ll note that 312-591 is on their list.
phone systems don’t work if too many people call at once. Around here in NC we used to have a problem when it snowed. On some of those days you could not get a dial tone to call out.