The announcement of the first directory enquiries service for mobile phones today provoked fears for the privacy of those on its database.
The directory bills itself as the UK's first service which can connect individuals to millions of mobile numbers.
Connectivity, the company behind the service, said the 15 million numbers "generally" came from companies which collect them from customers in the course of business and which had permission to share those numbers.
At no time would the mobile numbers be disclosed, Connectivity said, adding that only people verified as being over 18 are included in its directory.
But Simon Davies, of Privacy International, said many people on the directory would have unwittingly agreed to have their number circulated by, for example, failing to tick a box on a market research form.
"There are fundamental privacy issues," he told The Times.
"People tend to enjoy selective disclosure (of their number) with mobile phones."
Connectivity CEO Raj Raithatha argued the service was "privacy-friendly" because it did not disclose numbers.
He said: "If you try to connect to someone, it's up to the individual to get that information exchanged, we won't disclose numbers without express permission."
The inclusion on the database of any children using a phone which appeared to belong to an adult would amount to a "very insignificant" number, he added.
Users will be able to access the service by phone or online, prompting a search of a database of UK mobile phone numbers.
If the search is successful the operator will call the recipient, who can accept or decline the call. If the call is not answered, the service user can leave a voicemail or send a text message with their contact details.
There will be no charge for an unsuccessful search online, while charges for accessing the service by phone are "comparable" with existing directory enquiries services.
People can make their mobile ex-directory by texting the letter 'E' from that phone, although standard network charges will apply.
The service goes live next week and can be accessed by phoning 118 800 or online at 118800.co.uk