Apple's iOS 4 is scheduled to go live tomorrow, June 21, and here's everything you need to know to update your iPhone or iPod touch.

iOS 4 default homescreen

The final release version of iOS 4 for iPhone or iPod touch hits tomorrow (iPad isn't coming until later this fall) and we'll post it up right on the front page the minute it's ready. Before you race to download, however, there are a few steps you want to go through to get ready -- to make sure you have the smoothest upgrade possible.

Check device compatibility

The 2009 iPhone 3GS and iPod touch G3 (64GB and 32GB) get the full update (except for iPhone 4 specific features like FaceTime that require different hardware). Multitasking, folders, wallpapers, unified inbox, multiple Exchange accounts, the whole shebang.

The 2008 iPhone 3G and iPod touch G2 (which includes the 2009 iPod touch 8GB) won't be getting multitasking, custom wallpaper, and Bluetooth keyboard support as Apple maintains the hardware isn't capable (they have slower CPU, GPU, etc.)

The 2007 original iPhone 2G and iPod touch aren't compatible with iOS 4.

If you're not sure which iPhone or iPod touch you have, check Apple's support pages. [iPhone, iPod touch]

Make sure you're running iTunes 9.2

You need iTunes 9.2 in order to activate iOS 4 (and the forthcoming iPhone 4). Apple released it last Wednesday so, if you haven't gotten it already, hit Software Update and download the latest, or get it directly from Apple. [iTunes 9.2].

(Developers, remember you have the option of updating via Xcode instead of iTunes).

If you've Jailbroken, re-virginize

Safe and sound, an ounce of prevention, etc. etc. make us feel safer restoring a Jailbroken iPhone to 3.1.x before attempting to upgrade to iOS 4. You may not have a problem, but we've heard from enough readers who have for us to include this step.

And remember, updating to iOS 4 will mean no Jailbreak, no unlock for now. If that's a deal breaker for you, don't upgrade.

If you need extra help with this step, we've got a thread up in the TiPb Jailbreak Forum just for you.

Update your apps

One of iOS 4's biggest new features is multitasking, especially saved state (so your apps restart where you left them), and background audio, location, and VoIP (so you can listen to streaming music, get turn-by-turn directions, and answer internet phone calls even when not in the apps). However, developers have to update their apps for iOS 4 compatibility. That means new versions will be showing up in iTunes on the desktop or App Store on your iPhone/iPod touch, and that means you'll have to update to them.

Depending on how fast developers get the updates done, how fast Apple approves them, how many apps you have, and how big they are, this process could take a while. Might as well get started while you're waiting.

(We're keeping an eye out for major iOS 4 apps and compatibility updates so bookmark that link for future reference).

Backup your data

Once you have iTunes installed, plug in your iPhone and/or iPod touch and sync it. You want your data backed up, anything you've purchased or updated on-device transferred safely to your Windows/Mac library, and the position of any media you're currently enjoying recorded so you can keep going from the same place once your iOS 4 update is done.

Remember, if you haven't synced in a while it could take a few minutes to backup. Don't be impatient, let it run.

Once that's done, launch iPhoto on your Mac or your favorite image capture program on Windows and copy over any photos you've taken on the iPhone. Losing your Camera Roll, especially if it has a lot of special moments recorded, is something to be avoided at all costs.

Get up to speed on iOS 4

Once everything is done and ready, and if you're still waiting for Apple to release the update, why not check out our complete iOS 4 walkthrough so once you've downloaded and installed it you can spend your time enjoying the new functionality, not trying to discover it.

Jump into the forums and learn more

Did we mention how smart TiPb forum members are? If you have any lingering questions or need any additional help, or you just want to relax and chat with like-minded iOS enthusiasts and technology adepts, head on over to the TiPb iPhone Forum.

Best community on the 'net, check it out.

Anything else?

Did we forget anything or just plain get something wrong? Any tips or tricks you use before updating to a major new version of iOS? Let us know in the comments and we'll update.