Apple advertises up to 9 hours of WiFi browsing on the 3GS with all settings default. I've never gotten much over 6 hours with the same settings, personally. That's 30% less than advertised. With up to nine hours, one should reasonably expect 8 hours and change, in my opinion. My concern is that the iPhone 4 is supposed to get up to 10 hours of WiFi browsing but it will be more like 7 hours.