From reading the website, it looks as though they send a text message to the phone of the person being enquired after - which costs the enquirer £1. The text contains the details of the enquirer and invites the person being enquired after to make contact. Cold texting at £1 a time - with a strong possibility of the text not being acted on - doesn't sound a profitable proposition.

The only thing that's odd, to me, is saying that you have to be ex-directory by a certain date. You should be able to become ex-directory, like landlines, at any time.