Samsung beefs up the Galaxy S4's optical sensors in two major ways and in a couple of minor ways too. Firstly, the Galaxy S4's rear camera has a 4X digital zoom and can collect 13 million pixels; that's an enormous amount of information. The Galaxy S3's rear camera came with an 8MP rear camera. Both smartphones can capture 1080p video at 30 frames per second on their rear cameras, but the 1.9MP camera of the Galaxy S3 is limited to 720p video. Not only can the Galaxy S4 capture 1080p video on its 2.1MP front camera, it can also record video (or take pictures) on both cameras at the same time.
As for radios, the two models are nearly identical. Both smartphones offer near-field communications (NFC), introduced by Samsung with the Galaxy S3, as well as Bluetooth 4.0 and Wi-Fi a/b/g/n. Both also offer dual-band Wi-Fi, DLNA, Wi-Fi Direct and hotspot capabilities. And aside from the carriers previously mentioned, it seems a safe bet that the Galaxy S4 also will be available from Cricket, C-Spire and MetroPCS, as Galaxy S3 is now.