Now that Apple has made the Find My iPhone feature of Mobile Me free, many have decried that they cannot set up older devices with the service. Technically, that’s incorrect. However, you DO need one of the more recent, “blessed” devices to make it happen…
To get all of your iDevices registered and working, just create your Mobile Me.com account (at http://me.com) and connect an iPhone 4, iPad, or iPod Touch 4G as per Apple’s directions. Once you have done that, you can add all your other devices as well. Apple even says so; see the footnote at the bottom of http://www.apple.com/ipodtouch/features/find-my-ipodtouch.html:
You can create a free Find My iPhone account on any iPhone 4, iPad, or iPod touch (4th generation) running iOS 4.2. Once you create an account on a qualifying device, use your Apple ID and password to enable Find My iPhone on your other devices running iOS 4.2.
Step by step:
1. Download the “Find My iPhone” app from the App Store on to an iPhone 4, iPad, or 4th Gen iPod Touch.
2. Login to your existing Mobile Me account or create a new one in the app.
3. Repeat with all your other devices.
I can attest that this worked for me – my account now has an iPad, iPhone 4, iPhone 3GS, iPhone 3G, and an iPod Touch 2nd Gen all working well.