Upgrading iPhone 3Gs OS 4

OS 4 is not out yet. It is only in beta for registered developers.

When it becomes available this summer, you will be able to update to it in iTunes.

Question: What if OS 4 is released while on vacation abroad, is it then possible to upgrade on an "unknown" computer? Wouldn´t want all my contact info to be deleted in another country. All the topics I find on this is only about syncing, does it work in the same way for upgrading?

I would wait and do it when you got home. If something went wrong during the upgrade, you would be without a phone until you got back to your own computer.

You can upgrade software or restore an iphone on any computer. What you don't want to do is sync, except to the computer you normally sync with. So, make sure that auto sync when an ipod/iphone is connected is disabled under preferences in itunes BEFORE you connect your phone. Preferences is under the edit menu if using windows. Then connect your phone, DO NOT SYNC OR HIT THE SYNC BUTTON, rather hit the update button. When finished, eject your phone.

Thank you very much, wjosten

This was the one straight forward clear answer I have been searching for a while now.
I suppose that you have tried this and know by experience that it works. It seems that you know what you´re talking about anyway. And I was assuming that it should work the way you describe, even though it doesn´t say clearly anywere.

And if I´m not mistaking, if I loose my contact info, I could always sync it back through MobileMe, right?

Thanks again. Looking forward to the update:)

You won't lose any data on your phone unless you sync to a computer that your normally do not sync too. The key is not to sync.

iOS 4 will be available for download on June 21 per Steve Jobs Keynote at WWDC given June 7.