pw4 wrote on Dec 17
th, 2008 at 2:35pm:
David_H wrote on Dec 12
th, 2008 at 12:24pm:
can the companies spot whether someone's used their real number to call or not?
Yes. The number that was dialled is provided to companies' phone systems with each incoming call that is offered. That's how DDI works - all incoming calls share the same (virtual) lines and the phone system needs to know the number dialled to ring the right extension, or to tell the network that the number is busy if all extensions allocated to the number are busy or DND. So a call dialled to the geo number can be routed to the 'foreign calls' department and the caller's number will show that it is not a foreign call.
I'd say that this is quite possible, on the more sophisticated systems that actually terminate the NTS numbers directly. For the vast majority of users, though, the operators switch 'translates' (hence the T in NTS) into the underlying geographic number of the subscriber, and it's that which is presented to the subscriber's PABX. And even then, it's only ISDN or VoIP connections that allow presentation of the DID number - standard analogue POTS lines only allow for the callers' ID to be presented**, as each line has it's own physical number (unlike the others, where numbers are not directly tied to an connection.)
Of course, it's quite possble for an NTS number to terminate on a particular number, and the published 'international' geographic number to be a completely different number. So, simply because of the lines/DID number that the call rings on they know pretty much which you dialed.
** There are suppliers (eg Flextel) who can provide you with a non-gegraphic number that presents the NTS number dialed in place of the callers' numbers, but then you've lost the information on who is calling, so it's only of limited application.