The iPhone 4 is the fourth iPhone and was introduced in June of 2010. It has a 5 MP camera with 720p HD movie recording and a front camera for video calling. The 3.5-inch display is the first so-called Retina display, the resolution is of 960 × 640 pixels. The iPhone 4’s design is very different from the previous 3GS: its housing is made of glass while a stainless steel frame acts as an antenna. It’s also significantly more angular than the 3GS and the case is much narrower. In addition, the iPhone 4 has the more powerful Apple A4 chip. Within 24 hours there were over 600,000 pre-orders and in 3 days they sold 1.7 million units.