You asked in the comments if in iOS 6 Apple kept the button to disable the 3G connection on the iPhone 4S and the answer is no. The button has disappeared, the iPhone 4S only works on 3G networks and the only problem, from my point of view, is that the autonomy will be affected. Deactivating 3G in areas with weak signal, during the night or when you are connected to Wi-Fi networks significantly improves autonomy, but if you update to iOS 6 on iPhone 4S, you know that you give up this option.
UPDATE: It seems that the toggle has also disappeared from the iPhone 4.
