Rovio has made one its classic mobile games available on the iPhone, iPad and iPod touch available for free by slashing the prices of Angry Birds and Angry Birds HD to nothing for iOS users in both the United States and United Kingdom. It is unclear if this is a permanent move or just a limited-time offer, however Rovio also removed the free demo versions of the apps, which were limited to only a few levels. Since debuting in 2009, the Angry Birds franchise has found great success and the games have been downloaded more than 1 billion times.
Quoted from Original Angry Birds now free for iPhone, iPad and iPod touch on Gadgets News Headlines – Yahoo! News