On a purely usability point of view, I would suggest not displaying the phone number directly in the page. By all means display name and location details, but if the vultures are just collecting phone numbers, then adding a link that will send the full details via email may help. I guess that the type of person that might use this service would not object to having to receive an email (or how about via SMS thru an email gateway), but anyone looking to capture dozens of contacts will get fed up with having to do this for every contact ? Just my 2cents worth..

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