“Extension” - is the extension of the telephone line (PBX) or the Centrex system. It works as an association and allows calling to certain telephone sets without the necessity of dialing the telephone number, but only by dialing a short combination of digits, reaching the desired subscriber.
nfon is an IP-Centrex provider for enterprise customers. As the German market leader, nfon offers its technology also as a white label solution to other providers.