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.

NPA: 303 [Rate centres in NPA 303] [Dial plan for NPA 303]

NXX: 531

NPA-NXX BLOCK Rate Centre Region Switch OCN LATA LIR Eff date Disc date
303-531 A Denver CO DNVRCO37DS0  7229 MCIMETRO ACCESS TRANSMISSION SERVICES LLC 656      
303-531 0 Denver CO   026D ONVOY, LLC - CO 656   2007-09-06   
303-531 1 Denver CO   7229 MCIMETRO ACCESS TRANSMISSION SERVICES LLC 656      
303-531 2 Denver CO   026D ONVOY, LLC - CO 656   2007-09-06   
303-531 3 Denver CO   7229 MCIMETRO ACCESS TRANSMISSION SERVICES LLC 656      
303-531 4 Denver CO   026D ONVOY, LLC - CO 656   2002-07-24   
303-531 5 Denver CO   026D ONVOY, LLC - CO 656   2002-07-24   
303-531 6 Denver CO   026D ONVOY, LLC - CO 656   2002-07-24   
303-531 7 Denver CO   026D ONVOY, LLC - CO 656   2002-07-24   
303-531 8 Denver CO   026D ONVOY, LLC - CO 656   2002-07-24   
303-531 9 Denver CO   7229 MCIMETRO ACCESS TRANSMISSION SERVICES LLC 656      

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

Sponsored by: ISP Telecom

Like this site? We accept donations via PayPal.