# Why 591 for Chicago Radio Station Call-Ins?

**URL:** <https://boards.straightdope.com/t/why-591-for-chicago-radio-station-call-ins/764596>\
**Category:** Factual Questions\
**Created:** [August 31, 2016, 7:28pm UTC](https://boards.straightdope.com/t/why-591-for-chicago-radio-station-call-ins/764596 "2016-08-31T19:28:35Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![tesuji](https://avatars.discourse-cdn.com/v4/letter/t/85e7bf/32.png) [@tesuji](https://boards.straightdope.com/u/tesuji)\
**Post date:** [August 31, 2016, 7:28pm UTC](https://boards.straightdope.com/t/why-591-for-chicago-radio-station-call-ins/764596/1 "2016-08-31T19:28:35Z")

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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?

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**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\
**Post date:** [August 31, 2016, 7:49pm UTC](https://boards.straightdope.com/t/why-591-for-chicago-radio-station-call-ins/764596/2 "2016-08-31T19:49:23Z")

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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.

> **[Choke exchange](https://en.wikipedia.org/wiki/Choke_exchange)**
>
> A choke exchange is a telephone exchange designed to handle many simultaneous call attempts to telephone numbers of that exchange. Choke exchanges are typically used to service telephone numbers of talk radio caller and contest lines of radio stations and event ticket vendors.
> A central office might only have physical plant resources to handle ca. 8% of allocated telephone numbers, based on historical call traffic averages. A choke exchange has trunk facilities to other exchanges designed in a m...

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**Author:** ![Bijou\_Drains](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bijou_drains/32/2814_2.png) [@Bijou\_Drains](https://boards.straightdope.com/u/Bijou_Drains)\
**Post date:** [August 31, 2016, 8:53pm UTC](https://boards.straightdope.com/t/why-591-for-chicago-radio-station-call-ins/764596/3 "2016-08-31T20:53:00Z")

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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.