I picked up the optimus s yesterday and I kept getting the network error as well when trying to enable hotspot. Come to find out all you need to do is download a wifi tether widget to turn it on and then it will activate it. The widget I downloaded is called share switcher. Sprint will not charge $30 for the mobile hotspot since that only applies to 4G phones.... awsome phone!
actualy that applies to all devices the lg optimus s has a glitch in the software that alows hotspot to be activated via a widget. hotspot is avalible through sprint for that phone for 30$ a month. may i ask what software vierson you are on because this is what makes the difference.they fixed it on the software release on feb 7th