So which iPhone had the most upgrades compared to the previous model? So its iPhone 3G compared to the original iPhone, iPhone 3GS compared to the iPhone 3G, etc. I quickly made a list of some key features (yes this isn't the full list). iPhone 3G - 3G - GPS - Accelerometer - flush headphone jack iPhone 3GS - Voice Control - Faster processor - 7.2 HSDPA - 3MP camera with 480p video - Magnetometer and Compass iPhone 4 - All-new design - Retina display - A4 chip - Gyroscope - 5MP camera with LED flash - 720p HD video recording - FaceTime - Verizon & Sprint iPhone 4S - Siri - A5 chip - 8MP iSight camera - 1080p HD video recording - HSPA+ and World phone - AirPlay Mirroring - Bluetooth 4.0 - 64GB storage iPhone 5 - Thinnest & lightest design - 4-inch Retina display - 4G LTE - A6 chip - FaceTime HD camera with 720p HD video - Enhanced audio - Lightening connector I have to say that the iPhone 4 shows the biggest improvement compared to the iPhone 3GS. iPhone 4 introduced Retina display, Apple's own A4 chip, FaceTime, 5MP camera with 720p HD video, and more carrier options. Would like to hear other opinions.