On October 24, 2021, area code 309 was transitioned to ten-digit dialing, despite not being part of an overlay numbering plan, in which multiple area codes are assigned to a numbering plan area. The area code had telephone numbers assigned for the central office code 988. In 2020, 988 was designated nationwide as a dialing code for the National Suicide Prevention Lifeline, which created a conflict for exchanges that still permitted seven-digit dialing.
