The following is a preservation of a catalog of the former Number 4 Electronic Switching System (#4ESS) Class 4 Tandems that served the AT&T long distance network from 1976 to 2026. As of early 2026 there are no longer ANY #4ESS tandems in the network. This is the list that was maintained by the late telephone historian and researcher Mark Cuccia (1961-2014). The current list of AT&T Class 4 tandems are located on the AT&T N4E Tandem List.
The #4ESS switch was first installed in Chicago, IL in 1976 as the successor to the 4A crossbar switch. Between 1976 and 1990, nearly 140 #4ESS switches were installed in the PSTN. 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, the 4ESS tandems were starting to be supplemented by a new kind of tandem called the Next Generation 4ESS or N4E. The N4E emulates the #4ESS software in a new hardware environment.
One by one, the 4ESS tandems started to leave the network. 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. The last #4ESS in the network was in Anchorage, AK (139-T) and left the network in early 2026.
Classic 4ESS Tandem List. This is for HISTORICAL PURPOSES ONLY! Note: There are no more 4ESS tandems in the network as of March 2026. NSN Tandem Location CLLI Code Install date Special Uses 001 WINDERMERE FL WNDRFLTL01T (03/1991) 002 ALBUQUERQUE 2 NM ALBQNMMA02T (11/1977) MEX 003 ALBANY 3 NY ALBYNYSS05T (01/1982) 004 ANAHEIM 3 CA ANHMCA0211T (03/1981) 005 ARLINGTON 3 VA ARTNVACK04T (04/1982) 006 ATLANTA 5 GA ATLNGANW05T (03/1982) 007 ATLANTA 4 GA ATLNGATL01T (01/1977) OVS/ATL, CRB 008 AUSTIN 2 TX AUSTTXGR07T (01/1987) 009 BUFFALO 2 NY BFLONYFR05T (06/1984) CAN 010 BALTIMORE 10 MD BLTMMDCH01T (08/1980) 011 BIRMINGHAM 2 AL BRHMALMT01T (04/1981) 012 BATON ROUGE 2 LA BTRGLAMA04T (03/1984) 013 NEW YORK 5410 NY NYCMNY5410T (07/1991) 014 CHICAGO 9 IL CHCGILCL59T (08/1987) 015 CHARLOTTE 3 NC CHRLNCCA03T (05/1980) 016 CHARLESTON 2 WV CHTNWVLE25T (02/1982) 017 CLEVELAND 3 OH CLEVOH0203T (12/1979) 018 COLUMBIA 2 SC CLMASCTL03T (11/1981) 019 COLUMBUS 3 OH CLMBOH1103T (04/1977) 020 COLORADO SPRINGS 2 CO CLSPCOMA02T (10/1981) 021 CAMBRIDGE 19 MA CMBRMA0119T (12/1984) 022 CAMDEN 3 NJ CMDNNJCE03T (04/1979) 023 CINCINNATI 2 OH CNCNOHWS14T (06/1979) 024 DES MOINES 2 IA DESMIADT08T (06/1981) 025 DALLAS 3 TX DLLSTXTL34T (12/1976) MAS 026 DALLAS 4 TX DLLSTXTL44T (04/1981) 027 DENVER 5 CO DNVRCOZJ05T (11/1979) MAS 028 DETROIT 3 MI DTRTMIBH50T (04/1981) CAN 029 DAYTON 2 OH DYTNOH1504T (02/1987) 030 FREEHOLD 2 NJ FRHDNJ0202T (05/1978) 031 FRAMINGHAM 4 MA FRMNMAWA04T (05/1987) 032 FORT WORTH 2 TX FTWOTXED24T (02/1979) 033 GRAND RAPIDS 3 MI GDRPMIBL50T (05/1984) 034 GREENSBORO 3 NC GNBONCEU03T (03/1981) 035 GARDENA 3 CA GRDNCA0294T (06/1987) 036 HARRISBURG 2 PA HRBGPAHA42T (11/1980) 037 HOUSTON 4 TX HSTNTX0144T (01/1979) 038 HOUSTON 5 TX HSTNTX0154T (07/1988) 039 INDIANAPOLIS 2 IN IPLSIN0102T (10/1980) 040 JACKSON 2 MS JCSNMSPS14T (04/1983) 041 JACKSONVILLE 3 FL JCVLFLCL03T (12/1976) CRB 042 KNOXVILLE 2 TN KNVLTNMA71T (12/1980) 043 KANSAS CITY 2 MO KSCYMO0904T (07/1976) 044 LANSING 3 MI LNNGMIMN50T (05/1987) 045 LOS ANGELES 5 CA LSANCA0292T (02/1983) 046 LOS ANGELES 6 CA LSANCA0301T (04/1988) 047 LOUISVILLE 2 KY LSVLKYCS02T (07/1980) 048 LITTLE ROCK 2 AR LTRKARFR15T (02/1981) 049 MACON 3 GA MACNGAGA02T (04/1987) 050 MIDLAND 2 TX MDLDTXMU02T (10/1983) 051 MEMPHIS 2 TN MMPHTNMA43T (02/1981) 052 MANCHESTER 3 NH MNCHNHCO03T (04/1982) 053 (unassigned) 054 MINNEAPOLIS 3 MN MPLSMNDT18T (05/1980) CAN 055 MINNEAPOLIS 4 MN MPLSMNDT40T (06/1988) 056 MONTGOMERY 2 AL MTGMALMT01T (04/1978) 057 NORFOLK 4 VA NRFLVABS03T (04/1981) 058 NASHVILLE 2 TN NSVLTNMT43T (01/1978) 059 NEW HAVEN 5 CT NWHNCT0205T (10/1981) 060 NEW ORLEANS 3 LA NWORLAMA04T (06/1980) 061 NEWARK 8 NJ NWRKNJ0208T (06/1980) MAS 062 NEW YORK 24 NY NYCMNYBW24T (04/1978) 063 NEW YORK 51 NY NYCMNYBW51T (11/1984) 064 NEW YORK 5450 NY NYCMNY5450T (01/1981) 065 NEW YORK 12 NY(QUEENS) NYCQNYRP08T (08/1977) (Regal Park, QUEENS) 066 OJUS 3 FL OJUSFLTL03T (05/1978) 067 OAKBROOK 2 IL OKBRILOA52T (03/1981) 068 OAKBROOK 3 IL OKBRILOA53T (06/1988) 069 OKLAHOMA CITY 2 OK OKCYOKCE04T (05/1979) 070 OAKLAND 6 CA OKLDCA0344T (08/1981) (retire in 12/97?) 071 OMAHA 2 NE OMAHNENW14T (04/1979) 072 ORLANDO 3 FL ORLDFLMA03T (09/1980) 073 PEORIA 3 IL PEORILPJ51T (02/1983) 074 PHILADELPHIA 4 PA PHLAPASL42T (05/1980) MAS 075 PHOENIX 3 AZ PHNXAZMA03T (09/1980) 076 PITTSBURGH 3 PA PITBPADG43T (11/1977) 077 PORTLAND 3 OR PTLDOR6203T (04/1979) AK 078 RICHMOND 2 VA RCMDVAIT03T (05/1979) 079 ROCKY MOUNT 3 NC RCMTNCXA03T (06/1982) (was United-Carolina) 080 ROCHELLE PARK 3 NJ RCPKNJ0203T (08/1982) 081 RENO 4 NV RENONV0344T (05/1982) 082 SOUTH BEND 3 IN SBNDIN0502T (04/1987) 083 SACRAMENTO 4 CA SCRMCA0404T (10/1978) OVS/PAC, HI 084 SHERMAN OAKS 5 CA SHOKCA0296T (06/1985) OVS/PAC 085 STOCKTON 3 CA SKTNCA0107T (03/1984) 086 SALT LAKE CITY 2 UT SLKCUTMA02T (04/1982) CAN 087 SAN ANTONIO 2 TX SNANTXCA02T (05/1977) MEX 088 SAN DIEGO 3 CA SNDGCA0787T (04/1978) MEX 089 SAN FRANCISCO 4 CA SNFCCA2147T (06/1985) 090 SAN JOSE 3 CA SNJSCA0241T (03/1982) 091 SPRINGFIELD 2 IL SPFDILSD51T (04/1985) 092 SPRINGFIELD 3 MA SPFDMABR02T (05/1980) CAN 093 SPOKANE 2 WA SPKNWA0102T (10/1982) CAN 094 SAINT LOUIS 3 MO STLSMO0934T (05/1980) 095 SEATTLE 4 WA STTLWA0604T (05/1980) CAN, AK 096 SYRACUSE 2 NY SYRCNYSU13T (03/1985) 097 TAMPA FL TAMPFLCO02T (11/1986) 098 TOLEDO 2 OH TOLDOH2103T (04/1984) 099 TULSA 2 OK TULSOKTB04T (06/1980) 100 WASHINGTON 6 DC WASHDCSW06T (03/1978) 101 WAYNE 2 PA WAYNPALA42T (09/1977) 102 WICHITA 2 KS WCHTKSBR24T (04/1981) 103 WHITE PLAINS 3 NY WHPLNY0203T (01/1987) OVS/ATL 104 WHITE PLAINS 5 NY WHPLNY0504T (08/1980) CAN 105 WAUKESHA 3 WI WKSHWI0231T (03/1979) 106 WEST PALM BEACH 4 FL WPBHFLAN04T (08/1981) CRB (all below were installed after Summer 1988) 107 AKRON 4 OH AKRNOH2505T (04/1989) 108 ATLANTA 7 GA ATLNGATL04T (11/1988) 109 BLOOMINGTON 2 IN BLTNIN0144T (11/1989) 110 CHICAGO 11 IL CHCGILCL11T (01/1990) MAS 111 NEW YORK 55 NY NYCMNYBW55T (11/1988) OVS/ATL, CRB 112 PLYMOUTH 2 MI PLMOMIFA50T (12/1989) 113 SAN BERNARDINO 2 CA SNBRCA0101T (03/1989) 114 TUCSON 3 AZ TCSNAZMA03T (10/1989) 115 PITTSBURGH 9 PA PITBPADG09T (12/1988) OVS/ATL, CRB 116 OMAHA 3 NE OMAHNETU24T (07/1990) 117 HAMILTON SQUARE 2 NJ HMSQNJHS03T (07/1991) 118 WORCESTER 3 MA WRCSMA0204T (12/1991) 119 CHESHIRE CT CHSHCT0204T (01/1992) 120 NEW YORK 25 NY NYCMNYBW25T (02/1992) 121 HILLSBORO MO HLBOMO0134T (05/1992) 122 FINKSBURG MD FNBGMDFB01T (07/1992) 123 ADAMS TX ADMSTX0101T (10/1992) 124 PLANO IL PLANILLL01T (12/1992) STANDBY/TANDEM 125 ELLISVILLE FL ELVLFLMA01T (10/1992) 126 MONTICELLO 2 GA MNTIGAMA01T (10/1992) 127 CEDAR KNOLLS 2 NJ CDKNNJCK04T (10/1992) 128 TACOMA 2 WA TACMWA0202T (12/1992) 129 DUNNIGAN CA DNGNCA0101T (06/1993) 130 GARDENA 4 CA GRDNCA0201T (04/1993) 131 FORT LAUDERDALE FL FTLDFLOV01T (05/1993) 132 MADISON 3 WI MDSNWI0231T (11/1992) 133 WHITE PLAINS 4 NY WHPLNY0204T (08/1993) 134 MARKHAM ON (905-U2) MRHMONBD41T (06/1993) UNITEL (Canada) 135 CHERRYVILLE NJ CHVLNJQA01T (05/1993) 136 CAMBRIDGE MA CMBRMA0101T (06/1993) 137 ALDERGROVE BC (604-U2) ARGVBCAA41T (08/1993) UNITEL (Canada) 138 OXNARD CA OXNRCA0101T (07/1993) 139 ANCHORAGE AK ANCRAKZA01T (03/1996) ALASCOM 140 MESA AZ MESAAZTL01T (1998/1999) 141 DURHAM NC DRHMNCRT01T (1998/1999) 142 DENVER 6 CO DNVRCOMA16T (1998/1999) 143 FORT MYERS FL FTMYFLMA01T (1998/1999) 144 MONROVIA MD MNRVMDMO01T (1998/1999) 145 CHICAGO IL CHCGILCG51T (1998/1999) 146 ATLANTA GA(NW/CobbPkwy)ATLBGACA01T (07/1999) <- LAST #4ESS, EVER! MAS = Mass Announcement System CAN = US <-> Canada Gateways MEX = US <-> Mexico Gateways AK = US <-> Alaska Gateways HI = US <-> Hawaii Gateway CRB = US <-> Caribbean Gateways OVS = US <-> Overseas Gateways (ATL = Atlantic Area: Europe, Latin America, Africa, Western/Southern Asia) (PAC = Pacific Area: Austral-Asia/Orient/Pacifc Islands/Oceana)