ANI - automated number identification
ARS - automatic route selection
ATB - all trunks busy
BOC - Bell Operating Company
CD - call direct
CO - central office
COCOT - customer owned coined operated telephone
COS - class of service/class mark
DDD - direct distance dialing
DTEO - dial tone end office
EC - exchange carrier
FAB - features, advantages, benefits
FCC - Federal Communications Commissions
FGA - feature group A
FGB - feature group B
FGD - feature group D
FX - foreign exchange
HGA - hunt group arrangement
IC - interchange carrier
IDD - international direct dialing
IMT - inter-machine trunk
IOT - inter-office trunk
KSU - key service unit
LCO - least central office
LCR - least cost routing
MIW - microwave
MOU - minutes of use
MTS - measured telephone services
MU - message unit
NNX - net numbering exchange
NPA - numbering plan area/synonymous with area code
NTN - national telecommunications
NXX - three digit location code of seven-digit network number used for network dialing. N is a digit between "2" and "9" and X is any digit "0" through "9".
OCC - other common carrier
ONAL - off net access line
OPX - off premises extension
PABX - private automated branch exchange
PBX - private branch exchange
PIC - preferred interexchange carrier
PIN - personal identification number
POP - point of presence
PSC - Public Service Commission
PSN - public switched network
PUC - Public Utility Commission
RBOC - Regional Bell Operating Company
SCC - specialized common carrier
SEO - subscriber end office
SMDR - station message detail recording
STS - shared telecommunication service
SWC - serving wire center
TELCO - telephone company
TOD - time of day
UCD - uniform call distribution
WATS - wide area telecommunications service
XXXX - destination number
