The only differences between these two technologies is LOCATION. If  the location of the telephone switch is at the Customer Premise then it is called “PBX”. On the other side if the location of switch is in the Central Office, then it is called “Centrex”

Source:

T101 Telecom 101 – 4th edition 2016
7″ x 9″ softcover book • 488 pages • 4th edition • published 2016
ISBN 9781894887038 (print)   ISBN 9781894887786 (eBook)