What with all the excitement around iOS 4.2’s new features such as multi-tasking  and folders (on the iPad) and Air Play (all devices) and wireless printing (all devices), not enough attention is being paid to what is possibly the most valuable new feature: Find My iPhone (or other device) which is now free of charge.

The feature was previously only available as part of the $100/year Mobile Me subscription package. Now that it’s free, I strongly suggest you take the few quick steps that are required to enable it on your device – there’s no telling when you might need it and it isn’t turned on by default.

Now I hate to do this to you if you just read the above and got all excited, but here’s the bad news: The free service is only available for current generation devices (iPhone 4, iPad, iPod Touch 4th gen). All other devices can still use the service, but they need the paid Mobile Me subscription.. I know, it sucks :-(

Here are the links to the full set of instructions for iPhone, iPad and iPod Touch devices. But in a nutshell, you simply:

• Set up a free Mobile Me account using your existing Apple ID (this is your iTunes/App Store ID)
• Configure your device to allow location-based services
• Verify your Mobile Me account
• Log on to www.me.com to try it out

As with any service like this, there are a couple of provisos, specifically:

• Your device must be powered on
• Your device must be connected to the internet either by Wi-Fi or 3G
• Your device must be in a geographic area where the service is supported (some countries don’t support it)

If this is not the case, you won’t be able to locate your phone.

Another cool aspect to the Find My iPhone tool is the ability to force the device into “locked” mode (but only if you’ve assigned a Passcode previously), wipe the entire contents of the device remotely (you’ll be able to restore all of it from the backup on your PC if you get your device back) and – perhaps most useful of all –  you can send a message to the device that will appear on its screen and play a sound for two minutes (this works even if the device is locked and even if it’s set to mute).

This last feature will appeal to people who routinely misplace their devices but can always find their way to a computer.

Happy finding!