Originally Posted by og
They just bought the CD from the White Pages with the digital phone book. Same as the Taxi companies that magically know where you are calling from. That won't work if your calling number is blocked from transmission.
If this is a concern (and I don't think it is), it's easy to avoid by using a public phone or someone else's phone or a mobile not listed in the White Pages. This is why they could never charge a fee just for enquiring, although they may well want to.