To find your iPhone’s UDID, just plug it into your computer and wait until iTunes recognizes it. Please note that a Firewire iPod cable will not work, since the iPhone does not have the proper hardware to support firewire connections. Select your phone from the Devices list in iTunes and click the “Summary” tab. To see your UDID, click on the word “serial number” beside the picture of the iPhone. You should see the word “identifer” and an alphanumeric string – this is your UDID.

Alternative: You can also download an app from the Apple Store called Ad Hoc Helper which is a free download. Here is the itunes store URL http://phobos.apple.com/WebObjects/MZStore.woa/wa/viewSoftware?id=285691333&mt=8

To copy it, just press command + C on your Mac’s keyboard (or control + C in Windows). Now comes the hard part: getting on a developer’s beta testing list.