Dragon Collection was released on GREE on September 14, 2010, meaning it took 780 days to reach the 7 million user milestone.
To commemorate the milestone, the company not only started a number of in-game campaigns but also released a Dragon Collection iOS app today. That app comes with an opening movie and sound effects (whereas the original version is completely silent), amongst other things:
The game recently became available in the Canadian App Store (in English), too.
Via Social Game Info