"A late 2007 report in U.K.'s The Times said around 35 million R4 units are circulating, a number that has assuredly grown sharply since then."

Donc depuis 2007 les 35 millions ont probablement du monter un peu, on va dire entre 40 et 50.

Source : Gamasutra : http://www.gamasutra.com/php-bin/news_index.php?story=23529