The original iPhone was released on June 29, 2007. In the first month on sale (Jul 2007), it sold 2.315 million units. On July 11, 2008, the iPhone 3G was released which, hence the name, got upgraded with 3G wireless internet. On June 17, 2009, Apple released the iPhone 3GS which featured a compass and a 3.2-megapixel video camera. On June 24, 2010, a new version of the iPhone, the iPhone 4, was released. It has the Face Time-camera included, which is placed on the screen side and allows taking self-portraits while looking at the viewfinder. The Face Time-camera is less advanced than the back camera, but can be used for video-telephony, where the members of the talking can see each other on the screen. Additionally, it has an updated operating system that allows quicker navigation of all the features. This operating system is called IOS. The iPhone 4 also has more pixels (326 ppi; 960×640) on the screen than previous version of the iPhone, which makes all features such as pictures and videos look sharper. A minor upgrade to the iPhone 4 was the iPhone 4S. It came on October 14, 2011, and had a new feature called Siri, which is a voice activation system. Additionally, it is able to record videos in 1080p-FullHD-resolution, which is 2.25× times higher than 720p, so that each still frame from the video contains more details. This makes it possible to see smaller items on the footage in a sharper, clearer way. Additionally, it allows zooming into the video to see more details.