Local Calling Guide

Area code/prefix search

Search area code/prefix (NPA/NXX)
  • Effective date searches are available only for US area codes. Our sources for non-US NPA-NXX data do not provide this information.
  • If you want to search an entire area code regardless of activity, leave both the next and past days fields set to zero.

Switch: CHCGILMODS0

NPA-NXX BLOCK Rate Centre Region OCN LATA LIR Eff date Disc date
312-421 A Chicago Zone 01-Monroe IL 9329 ILLINOIS BELL TEL CO 358      
312-433 A Chicago Zone 01-Monroe IL 9329 ILLINOIS BELL TEL CO 358      
312-491 A Chicago Zone 01-Monroe IL 9329 ILLINOIS BELL TEL CO 358      
312-572 A Chicago Zone 01-Monroe IL 9329 ILLINOIS BELL TEL CO 358      
312-633 A Chicago Zone 01-Monroe IL 9329 ILLINOIS BELL TEL CO 358      
312-738 A Chicago Zone 01-Monroe IL 9329 ILLINOIS BELL TEL CO 358      
312-829 A Chicago Zone 01-Monroe IL 9329 ILLINOIS BELL TEL CO 358      
312-850 A Chicago Zone 01-Monroe IL 9329 ILLINOIS BELL TEL CO 358      

Last updated: Tue, 13 Jan 2026 21:50:02 UTC

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