They're not the first; Path Intelligence tried it in 2007: http://techcrunch.com/2007/12/14/path-intelligence-monitors-foot-traffic-in-retail-stores-by-pinging-

They're not the first; Path Intelligence tried it in 2007: http://techcrunch.com/2007/12/14/path-intelligence-monitors-foot-traffic-in-retail-stores-by-pinging-peoples-phones/ http://techcrunch.com/2007/12/14/path-intelligence-monitors-...