Had a chance to compare my iPhone 4 with my friend's 4S this weekend. A few subtle differences we noticed (they've probably been noted here already, but thought I'd pass them along anyway just in case): - The speaker is better. This was very obvious when we played identical mp3s in the 'Music' app. For ringtones and text tones, the iPhone 4S appeared louder, but it was not as pronounced as when we were playing music. - The vibrate has changed. The 4S vibrate makes less sound but vibrates just as hard if not harder. If it is in your pocket during class/work, this is a welcome change.