I wouldn't upgrade if you have 3.1.2 or 3.13 for the 3Gs and if you have a 3G never upgrade to 4.0 because it will slow down your iphone 3G even more than it already is with 3.1.2 or 3.1.3 If you already downloaded 4.0 like I did a real dumbass move on my part thinking 4.0 would be better on my 3GS which it isn't. I now have signal issues I didn't have before and dropped calls and Internet. do not download 4.0.1 or whatever the hell it is either, it's a fix from 4.0??? Yeah whatever. Going back to 3.1.3 would be the true fix but apple won't let you. Won't let you choose which program you have on your iPhone that you bought and own and that works best for you. Very good company!!! Top notch support. I'm sure downloading the 4.0.1 latest version will cause you some kind of grief on your 3GS so stay away from it. If you have 3.1.3 or older be thankful and keep it . I deleted iTunes off my computer to. Another good move.