with 30 user-inspired levels was added. On June 23, 2015, Flock Favorites was added with 15 levels inspired by previous episodes. On December 11, 2015, in honor of Angry Birds 6th birthday, new 15 levels were added to Birdday Party. On December 11, 2016, in honor of Angry Birds' seventh birthday 15 more levels were added to Birdday Party. On May 16, 2017, a dual virtual currency system was added to the game, in which currency is earned throughout gameplay (or accrued through in-app purchases) and can be used to purchase power-ups and other in-game items. Ports Since its initial release for the Nokia N900 multimedia Internet device, and Apple's iPhone and iPod Touch mobile digital devices, Rovio has released versions of Angry Birds for additional devices. An iPad-exclusive version, Angry Birds HD, was released with the iPad mobile digital device in April 2010. In August 2010, Angry Birds was made available to the Palm Pre phone running Palm's webOS operating system through its App Catalog online store. Symbian^3 phones received a version of the game in October 2010, which initially includes only the "Poached Eggs" and "Mighty Hoax" episodes. Angry Birds works on Kindle Fire and Kindle Fire HD. In May 2010, Rovio announced plans for a version for devices using Google's Android operating system, with a beta version being released through the Android Market (now Google Play) in September 2010. The full Android version of the game was first released instead on GetJar in October 2010, though it was subsequently released on Android Market within days. Rovio officials noted that GetJar had a more global reach than Android Market, and GetJar's availability on other smartphone platforms (including Symbian) would make cross-platform promotion of the game easier. Unlike the previous versions, Angry Birds for Android is a free, ad-supported application, as paid applications aren't available on Android in some nations. An update called "Bad Piggy Bank" enabled players to buy out the in-game ads. In October 2010, Microsoft suggested on one of its websites that a Windows Phone version of Angry Birds was in development. Rovio complained that Microsoft had not asked permission to make such a statement, noting that at that time it had not committed to design a Windows Phone version. Although Rovio asked Microsoft to revise its site to remove references to the game, a Windows Phone version was ultimately released in June 2011. Near the