Moving from iPhone 3GS OS 3.1.3 to iPhone 4

Question

I am planning to upgrade phones (as above). I have a few questions please:
1. I have never updated my 3GS, mostly out of paranoia of losing everything but also because the laptop I originally had my iTunes on crashed. I have only ever purchased songs directly from my phone iTunes app. Am I able to install and use iTunes on a different computer and it still recognize my old phone?
2. How do I backup my old phone before transferring?
3. How do I transfer everything from my old phone to my new one without losing anything?

Answer 1

The first thing you need to do is install iTunes on your computer.
Once that's done, if you're on a PC, in iTunes click on Edit > Preferences > Devices > check where it says "prevent ipads, ipods, and iphones from syncing automatically'
-or-
If you're on a Mac, click iTunes > Preferences > Devices > check where it says that same message
Now, when you plug your 3gs into the computer, it won't sync until you tell it to and your data won't get erased
Next, plug in your phone to your computer. Right-click on the name of your device on the left-hand side of iTunes and select where it says 'transfer purchases from (your phone)'
Next, right-click on the name of your device again and select 'back up your device'
Now all your data is on your computer, even your itunes purchases.
You will probably need to authorize your computer at some point, but it will prompt you to do so if necessary
Now when you get your new iPhone 4 and you go through the set-up process, it will ask you if you want to set it up as a new phone or restore it from an iTunes backup (which you will select)
Then you're all set up!
In the future, please do yourself a favor and backup your phone often. That way you can update your iOS as often as Apple releases updates. They're very useful and often make your phone run faster, have longer battery life, and fix bugs