It's an instant data transfer feature between two NFC-enabled devices, Just tap the two devices together to transfer music, contacts and even apps. There is no menu to open and no syncing or pairing needed, you just have to tap the screen to send. For sharing apps, Android Beam sends a link to the app's details page in the Android Market. On the other device, the Market app launches and loads the details page, to download it.
HTC Amaze also has a larger screen than the iPhone 4S and because it is 4G enabled, should be able to achieve faster upload and download speeds. Despite the smaller screen, iPhone 4S has a bit better resolution because of its very high pixel per square inch count. Also, in part due to its smaller screen size, iPhone 4S is thinner and lighter. It's made of glass and metal, but Amaze 4G is made of aluminum.
In this smartphone battle, which one you should get will depend on if you are a current T-Mobile customer or if you upgrading from a feature phone. If you are upgrading and are under T-Mobile contract, you'll love the Amaze 4G. If you're contract is up and you are upgrading from a feature phone, be sure to test out both and pick the one you like best.