Area code 872 is an overlay for both 312 and 773, covering all of Chicago, including downtown and surrounding neighborhoods. It was introduced in 2009 to relieve pressure on the existing codes and ensure continued number availability. The addition of 872 required ten-digit dialing throughout the entire city. While 872 is more common on newer phone lines, 312 and 773 remain more widely recognized and preferred for their legacy. Still, 872 has become a standard part of Chicago’s telecommunications landscape, helping support the city’s ongoing growth in residential, commercial, and mobile usage.