Apple has given developers a way to beta test iPhone applications with i think up-to 100 iPhones. Some developers have already started using this to their advantage by giving their software out as free public betas. However, you must supply a developer with your iPhone’s UDID (unique device identifier) in order to install these “Ad-hoc” applications on your iPhone.
Here is how you find your iPhone’s UDID, just plug it into your computer and wait until iTunes recognizes it. Select your iPhone from the Devices list in iTunes. Click on 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. If you click again, it will tonggle back to Serial Number.
To copy it, just press control + C in Windows (or command + C on Mac’s). Paste it to a Notepad to save your UDID.
If you click on the Software Version, for example 2.2.1, it will tonggle to Build Version like 5H11