A few minutes ago, we explained you how to set up Find My iPhone on your iPhone 4. Technically, the newly free Find My iPhone only works for the iPhone, iPad and iPod Touch running iOS 4.2. There is however a trick to make this work on older devices.
The funniest part is that Apple is even telling you how to bypass their own rules… From Apple’s Find My iPhone set up page, in the footnotes:
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. Find My iPhone is not available in all countries.
So basically, set it up on your iPhone 4 running iOS 4.2, then you can repeat the process on any other device running 4.2.