How can I un-jailbreak an iPhone 4? I have purchased an iPhone 4 about six-seven months ago. Roughly two weeks into using it I have decided to jailbreak the iPhone for ideological reasons (I am not a big fan of The Man telling me how to manage my stuff)

However, after all these passing months I can honestly tell that I have not even used any of the jailbreak features even once.

I recall jailbreaking erased my entire phonebook, SMS logs and all other data. Since that was only about two weeks without much usage - I didn't mind too much. This time it seems a bit more worrisome, as the phonebook and SMS contain a lot more information, some which I do not want to be lost.

I should mention that only part of my phonebook is synchronized with my google account (is there an easy way to transfer the rest?), and that I use Linux and a windows on VirtualBox where my iTunes fails to backup the data on my iPhone (this might be redeemable with some very hard work, though.)

My question, if so, is whether or not all my non-Cydia-and-otherwise-non iTunes-apps will be gone if I just run an upgrade through iTunes, and whether or not this upgrade is going to obliterate my phonebook and/or other databases?
As long as you backup your iPhone by syncing with iTunes, it'll restore every non-jailbreak thing just fine. The only exception being your login information for accounts and whatnot, unless iTunes is encrypting your backup.

You can verify your backup by going to iTunes' preferences and selecting the devices tab.

I'm not sure if it's still an issue, but if you happen to be using a tweak like "Five Icon Dock", you'll want to remove the extra icons from your dock, otherwise when you boot-up after restore, Springboard will constantly crash.