Although Apple explicated the iPhone 4’s biggest new features (A4 processor, “retina” display, gyroscope, front-facing camera, increased battery life, etc.), a few important albeit less-sexy features are also included in the model.
New HSDPA spectrum support. The iPhone 4 includes quad-band rather than tri-band HSPA connectivity. This means that the new iPhone runs on an additional frequency (900 MHz) in the UMTS/HSDPA spectrum. This means that the iPhone 4 should be able to take advantage of faster HSDPA speeds in geographies where carriers use the 900 MHz frequency: Europe, Asia, Oceania (Optus, Vodafone AU, Vodafone NZ), Venezuela (DIGITEL) according to this Wikipedia entry.
More video/audio formats support. The iPhone 4 supports H.264 video up to 720p (the iPhone 3GS maxed out at 640 by 480 pixels) and Main Profile level 3.1 with AAC-LC audio up to 160 Kbps (the iPhone 3GS supported only Low-Complexity version of the H.264 Baseline Profile with AAC-LC audio up to 160 Kbps).
The iPhone 4 also supports Motion JPEG (M-JPEG) up to 35 Mbps, 1280 by 720 pixels, 30 frames per second, audio in ulaw, PCM stereo audio in .avi file format.
It can also output 1024 by 768 pixels with a Dock Connector to VGA Adapter.
802.11n. The iPhone 4 includes 802.11n networking (the iPhone 3GS offered only 802.11 b and g), which offers theoretical data transfer rates up to 150 Mbps.