If you have an iPhone 4S terminal then you surely know that you cannot disable the device's 3G connection unless you do jailbreak and install a tweak like SBSettings. After installing such a tweak, you have the option to disable the 3G connection, but unfortunately that option is useless for the new terminal, even though Apple included it even in iOS 5.1. In a week of using the iPhone 4S, I chose to close the 3G connection several times, but unfortunately I found that the device automatically reconnects to it even if I force it to stay on 3G.
iPhone 4S was designed to work on 3G networks and even if you use a tweak like SBSettings or IntelliScreenX to switch it to EDGE mode, the device will automatically and randomly return to the 3G connection. Several times I set the iPhone 4S terminal on EDGE connection only to find it a few hours later connected to the 3G network even though I changed absolutely nothing through the settings and the device had a strong signal on the EDGE network. I don't know how Apple modified the iOS for the iPhone 4S, but it seems that the device necessarily only works on 3G networks, even if we don't want this.
I don't know if things will be the same in iOS 5.1, but some of those who installed the new version of iOS say that the device doesn't really remember when 3G is turned off.
