The following is a work in progress in trying to maintain an active catalog of the Number 4 Electronic Switching System (#4ESS) Class 4 Tandem list for the AT&T long distance network. This list is a successor to the original list made by the late telephone historian and researcher Mark Cuccia (1961-2014) to try to encompass the changes in the #4ESS network since his passing.
The #4ESS switch was first installed in Chicago, IL in 1976 as the successor to the 4A crossbar switch. Over 100 #4ESS switches were installed in the PSTN by the early 1990s for AT&T Long Lines, and a number of them were also used for the regional Bell operating companies. A second batch of #4ESS switches (what I call “2nd Generation”) were installed in 1998-1999 and were the last #4ESS switches installed in the PSTN, with the one in Atlanta (number 146-T) being the last one ever.
Starting in or around 2012, a new batch of #4ESS type Class 4 switches were starting to show up in the PTSN. This is the successor switch called the Next Generation 4ESS or N4E. The N4E emulates the #4ESS software in a new hardware environment. The main difference to the end user is that the tandem recordings are very clean (no magnetic drums) and sound a bit robotic in nature.
This list not only contains the #4ESSes in the network, but the new N4E switches as well. In some cases, there are N4E switches that are replacing 4ESS switches, and in some cases they are brand new to the network (those numbering 147 and higher). It is assumed that the new N4Es are replacing the #5ESS switches that were originally installed to be “edge tandems” in the AT&T network and upgrading them to full Class 4 tandems.
The locations for the new N4E switches (147 and higher) are best guesses, and in some cases appears to be replacing existing #4ESS switches and taking on new identities, while in other cases they take on the old trailer code (known as the Network Switch Number of NSN) of the #4ESS that they replaced.
By October 2025, there were about three or four traditional 4ESS systems still in service. The last #4ESS in the continental United States was Lansing, MI (044-T). Though traffic from that switch had been diverted elsewhere by late October, the switch itself was powered down on December 10, 2025.
Rumor has it that the #4ESS in Anchorage, AK is still around and will be decommissioned in 2026. That switch was originally a spare switch in Chicago, IL. By most accounts, that switch will be the very last #4ESS in the network.
Confirmed 4ESS or N4E - Survey as of October 2025 NSN Switch Name, ST Type Install Date Last Verified Date 007 ATLANTA 4 GA N4E Replaced Oct 2025 019 COLUMBUS 3 OH N4E Replaced Oct 2025 024 DES MOINES 2 IA N4E Replaced Oct 2025 027 DENVER 5 CO N4E Replaced Oct 2025 030 FREEHOLD 2 NJ N4E Replaced Oct 2025 032 FORT WORTH 2 TX N4E Replaced Oct 2025 034 GREENSBORO 3 NC N4E Replaced Oct 2025 037 HOUSTON 4 TX N4E Replaced Oct 2025 040 JACKSON 2 MS N4E Replaced Oct 2025 043 KANSAS CITY 2 MO N4E Replaced Oct 2025 048 LITTLE ROCK 2 AR N4E Replaced Oct 2025 056 MONTGOMERY 2 AL N4E Replaced Oct 2025 058 NASHVILLE 2 TN N4E Replaced Oct 2025 065 NEW YORK 12 NY(QUEENS) N4E Replaced Oct 2025 067 OAKBROOK 2 IL N4E Replaced Oct 2025 070 OAKLAND 6 CA N4E Replaced Oct 2025 071 OMAHA 2 NE N4E Replaced Oct 2025 076 PITTSBURGH 3 PA N4E Replaced Oct 2025 077 PORTLAND 3 OR N4E Replaced Oct 2025 078 RICHMOND 2 VA N4E Replaced Oct 2025 083 SACRAMENTO 4 CA N4E Replaced Oct 2025 084 SHERMAN OAKS 5 CA N4E Replaced Oct 2025 087 SAN ANTONIO 2 TX N4E Replaced Oct 2025 088 SAN DIEGO 3 CA N4E Replaced Oct 2025 089 SAN FRANCISCO 4 CA N4E Replaced Oct 2025 094 SAINT LOUIS 3 MO N4E Replaced Oct 2025 100 WASHINGTON 6 DC N4E Replaced Oct 2025 103 WHITE PLAINS 3 NY N4E Replaced Oct 2025 105 WAUKESHA 3 WI N4E Replaced Oct 2025 110 CHICAGO 11 IL N4E Replaced Oct 2025 111 NEW YORK 55 NY N4E Replaced Oct 2025 147 Chicago IL? N4E 2012? Oct 2025 148 Boston MA? N4E ? Oct 2025 149 Mesa AZ? N4E ? Oct 2025 150 Atlanta GA? N4E ? Oct 2025 151 Fort Myers, FL? N4E ? Oct 2025 152 Gardena CA? N4E 2012? Oct 2025 153 MA? N4E ? Oct 2025 154 Dallas TX? N4E ? Oct 2025 155 Scottsdale AZ? N4E ? Oct 2025 156 Buffalo? N4E ? Oct 2025 157 Jacksonville FL? N4E ? Oct 2025 158 Anaheim, CA? N4E ? Oct 2025 159 Wayne PA? N4E 2016? Oct 2025 Possibly still in service, but not 100% sure NSN Switch Name, ST Type Install Date Last Verified Date 129 DUNNIGAN CA N4E Replaced May 2023 Assumed disconnected, but not 100% sure NSN Switch Name, ST Type Install Date Last Verified Date 139 ANCHORAGE, AK 4ESS March 1996 April 2025