Happy iOS 4.2 Day! In case you haven’t heard, Apple has generously made one of the formerly subscription-only MobileMe services, Find My iPhone, now free for all owners of current-generation iOS devices. Here’s how to get it up and running -- even on an older device.

Find My iPhone always made an odd match with MobileMe, which requires a $99 annual subscription to use. Doesn’t Apple want every iOS mobile device user to be able to find their lost or stolen unit? Apparently they do, because Find My iPhone is now a free service, complete with an update to the existing universal iOS app and the ability to log in to Me.com using your Apple ID.

Unfortunately, the free edition of Find My iPhone requires a current generation iOS device -- which means, an iPhone 4, fourth-gen iPod touch or iPad. But fear not, MacLife.com is here to make the magic happen on any device you happen to own.

Install (or Update) Find My iPhone

The first step toward feeling secure that you can find a lost device is to head to iTunes (either on your computer or from the device itself) and download Find My iPhone 1.1, which was released on Monday alongside iOS 4.2. Apple notes that “this update is required for users of the previous version of Find My iPhone app (v1.0 and v1.0.1), so no sense delaying the inevitable.

Of course, you’ll also have to be running iOS 4.2 in order to take advantage of Apple’s generosity, so if you haven’t done so, plug your device into iTunes and get updated. (Jailbreakers beware: You’ll be restored to a stock iOS 4.2 install, so approach with caution.) Seriously -- go do it right now. We’ll wait.

Sign In with Your Apple ID

Okay, everyone on iOS 4.2 (which is actually iOS 4.2.1 if you want to be nitpicky about it) and have Find My iPhone 1.1 installed? Good, let’s move on.

Launch the Settings app and head into “Mail, Contacts, Calendars,” then add a MobileMe account. You’ll be greeted with a request to enter either your Apple ID or MobileMe e-mail address. In this case we want to enter our Apple ID, which is the same as the one we use to shop at the iTunes Store (you remember it, don’t you?). Type it in and move to the Password field, enter that and tap on Next. Apple will verify your credentials and you’ll be ready for the main event -- flip the switch to turn on Find My iPhone (or iPad, or iPod touch), tap Allow at the prompt and then Save to activate.

If you don’t have an Apple ID yet, prepare to run the gauntlet to get one: Tap on “Create Free Apple ID,” enter your Location and date of birth (Month, Day and Year), tap Next and then complete your e-mail address, first and last name, password and security question. Apple has beefed up security with iTunes passwords, now requiring at least eight characters, which must include a number and both an uppercase and lowercase letter. (Yikes!) You’ll also be presented with the first of 14 pages (?!) of Apple’s “MobileMe Free Account” terms of service. Accept that and the final hurdle remains -- verifying your new account from an e-mail you’ll receive and then logging into the new account online. Whew!

Launch Find My iPhone App

Now that iOS 4.2 recognizes you as a free user, you can launch the Find My iPhone app, where you’ll be greeted by the same request for Apple ID and Password.

This request was initially a conundrum for us, since our Apple ID and password happen to be the same as our MobileMe account -- when we entered our Apple ID and password, Find My iPhone threw back an error, even with the correct info. The solution is to turn off your paid MobileMe service, or login using your full MobileMe e-mail address (for instance, “ilovemaclife@me.com” instead of just “ilovemaclife”) to use Find My iPhone as part of your subscription.

In either event, once you log in, you’ll be presented with a list of devices, which at this point should only contain the device being held in your hand. You can add additional devices by repeating the instructions above on each one.

What About My Older Devices?

Ah, you were clearly paying attention earlier when we mentioned a trick to get your older iOS devices working with the free Find My iPhone service. For whatever reason, Apple has limited the free offering to the iPhone 4, fourth-gen iPod touch and iPad, but what if you have an iPhone 3G or 3GS that’s capable of running iOS 4.2 but can’t be activated?

The solution is amazingly simple -- although you’ll need access to one of the newer devices in order to make the magic happen. As it turns out, you can use a friend’s current-generation device to sign in using your Apple ID and password as outlined above. If they happen to be a MobileMe subscriber, you’ll need to turn off their existing account to take advantage of this tip.

With Find My iPhone activated on your friend’s device, repeat the process on your older handset -- you can confirm that things are working as expected by using the same credentials to log in at Me.com, where you’ll now see both your friend’s device as well as your own.

Once you’ve confirmed that things are working on your elder device, simply delete your friend’s device from your account on the same Me.com page (you can’t delete devices from the Find My iPhone app itself) and lo and behold, your aging device will continue to work absolutely free forevermore.

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