Area code 773
By the mid-1990s, Chicago's continued growth and the proliferation of cell phones and pagers made it apparent that the city needed a new area code. It was decided to split off all of the city outside the downtown area as 773. The new area code went into effect on October 12, 1996. Permissive dialing of 312 continued across Chicago until January 11, 1997.   On August 10, 2007, the Illinois Commerce Commission announced that area code 872 would overlay area codes 312 and 773; it went into service on November 7, 2009.
The Illinois side of the Chicago area–312/773/872, 708, 847/224, 630/331 and portions of 815/779–is one of the largest local calling areas in the United States. No long-distance charges are applied to most calls within the metro area. However, in-state long-distance charges are applied to calls to numbers over 15 miles away within the metro area. For example, a call from the Rogers Park exchange (773) 338-XXXX on the north side to a Pullman Exchange (773) 785-XXXX on the south side is billed as a long-distance call, even though both neighborhoods are within city limits. 
- "AT&T Area Code History: Illinois". AT&T. 2009. Retrieved August 19, 2009.
- Map of Illinois area codes at North American Numbering Plan Administration's website
- List of exchanges from AreaCodeDownload.com, 773 Area Code
- AT&T Local Calling Area Database
|West: 708||area code 773||East: 312, 219, Lake Michigan|
|Indiana area codes: 219, 260, 317/463, 574, 765, 812/930|
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