With iPhone OS 3.0 available now, there's a lot to consider. Do you want to upgrade immediately? And even if you want to... should you? When you upgrade, what steps can you take before -- and after -- to best ensure a positive, successful migration? We've put together this guide to help you answer exactly those questions. We've already updated it with one batch of post-release reports, and more will be coming. Please use the comments below to share your experiences and questions for everyone to read.

Should I Upgrade?

In short, yes. Why? It's free for iPhone owners (US$9.95 for iPod touch owners) and, going forward, you'll find apps and features that require iPhone OS 3.0 to function properly. That said, it's probably not a bad idea to wait at least a day or two for all the edge-case problem reports to come in -- but we know most of you won't wait a minute longer than you have to (we won't!). There are a lot of reasons to upgrade, and they include:

• Cut/Copy/Paste Functionality
• Device-wide Spotlight Search
• Faster Mobile Safari Performance
• Auto-fill for Mobile Safari
• Voice Memos
• (mostly) System-wide Landscape keyboard mode
• Push notification support
• In-App Purchase support
• Support for additional languages
• Find My iPhone for MobileMe customers

Update Your Apps First

Note that we said "update" in the section title, not "upgrade" (not yet!). The first thing you'll want to do is visit the App Store in both iTunes and on your iPhone and make sure you have the latest versions of all your apps. There's a good chance that the third-party apps you are using on your iPhone or iPod touch are iPhone OS 3.0-ready, but that also means there's a chance that at least a couple aren't. Before upgrading to the new OS, make sure you have the latest app versions installed. We have a Quick Tip to help you through the process.

Checking for OS 3.0-ready apps on your iPhone or iPod touch

While Apple is specifically labeling any apps that are certified for iPhone OS 3.0, most of those that haven't been tested will work just fine. That said, we suggest making a point of checking both the App Store and the developers' Web sites for any mission-critical apps you run, just to make sure you see the latest info about any 3.0-related pitfalls before you upgrade. If there's an app you simply cannot live without, we recommend delaying your iPhone OS 3.0 upgrade until that app has been certified to work in 3.0.

Backup, then Backup Again

Upgrading to iPhone OS 3.0, or any iPhone OS for that matter, will wipe out your phone and then restore it. Just like the data on your computer, the information on your iPhone or iPod touch could be forever lost if it isn't backed up. iTunes backs up your handheld's data every time you sync with your Mac or PC, so you should already have a copy of all your important information safely tucked away.

You can make doubly sure your iPhone data is protected by backing up your backup. If you already have a strong backup process in place, odds are your iPhone and iPod touch backups are included. If not, or if you aren't sure if your handheld data is included in your computer backup, check out our Quick Tip on backing up your iPhone's data.

Save Your Settings and Notes

While the upgrade to iPhone OS 3.0 shouldn't wipe out any of your settings, it's still a good idea to go into the Settings app and note anything you might not otherwise remember if things go south. An easy way to make sure you have an accurate record of all your settings is to use the screen capture feature to take snapshot pictures of your iPhone and iPod touch settings. We have a Quick Tip that details how to take iPhone screenshots and what to do once you have those pictures.

Along the same lines, we recommend emailing yourself any notes you can't afford to lose. To email a note to yourself, tap the Notes app icon, select the note you want to email, and then tap the envelope icon at the bottom of the screen.

Copy Your Data Back

After you upgrade to iPhone OS 3.0 there is a chance that some of the applications, music, or videos that you expect to see won't be there if, at some point, you told iTunes to stop syncing and disabled its warnings. Re-enabling warnings in iTunes will gives you the opportunity to transfer apps and media back from your iPhone that otherwise might get missed.

Resetting warnings in iTunes

To re-enable warnings for your iPhone or iPod touch, connect your handheld to your computer, Ctrl-click or Right-click on your device in the Library list, and then choose Reset Warnings from the pop-up menu. We have a Quick Tip that details the process, too. Once you've reset the warning, perform another sync, and iTunes will obediently display any warning dialogs that were previously hidden.

It's Upgrade Time!

Now that you've covered as many of your bases as is reasonable (and perhaps unreasonable but, hey, we're playing it safe!), go ahead and tell iTunes to install the upgrade to iPhone OS 3.0. This will take some time. Afterwards your phone will need to be reactivated online, so make sure you've got plenty of bandwidth (and battery power, if on a laptop) to get the job done.

Once the update is complete, go through your iPhone and make sure your settings are correct. The two places (so far!) that we suggest checking are Mail accounts and Calendars. Go into Settings > Mail, Contacts, Calendars and confirm that the Accounts section contains exactly (and only) what you want. Then scroll down to the bottom of that preference list and confirm that Default Calendar is also set properly. As more reports come in, we'll update this section with anything that seems to be affecting folks after they upgrade.

Post-Upgrade Advice

Most early reports are showing that the upgrades have been downloading and installing without a hitch. We do recommend you wait to do anything in iTunes until after your iPhone's display shows that it has completed an upgrade and the initial Sync.

Once you've upgraded your iPhone will, in theory, be fully functional complete with all the data that existed prior. In fact, you'll likely even find that all the web pages you had open in Safari are still there! Still, there are a few steps to take.  Because this upgrade completely replaces the firmware on your iPhone, the first Sync you perform after the upgrade will trigger a backup that will take a long time (upwards of 15 minutes for some people).  Because of this, we highly recommend doing that immediately so you're not tempted to skip it 3 days from now when you plug your iPhone in again for a quick sync before running out the door for work. Simply plug your iPhone back into your computer, let iTunes do its thing, and then you're off and running.

Have Fun!

Now it's time to have some fun playing with the new features in iPhone OS 3.0. Then come back and tell us, and the rest of your fellow TMO Observers, about it all in the comments.

[Updated June 27, 2009, 2:51pm EDT to reflect the release of iPhone OS 3.0 as well as adding the Post-Upgrade Advice section above.]