How can I force 3G only on the Nexus S after the ICS update?
There's an app for 3G only mode:


https://play.google.com/store/apps/details?id=com.mobnetic.only3G


However your phone should automatically try and go for 3G if there's a 3G connection available, it will never choose 2G over 3G so I don't see why this would be useful... There's still a 2G only mode to save battery in Settings -> Mobile Networks