What is the UDID?
Each iPhone or iPod Touch has a Unique Device Identifier (UDID), which is a sequence of 40 letters and numbers that is specific to your device. It’s like a serial number but much harder to guess. It will look something like this: 2b6f0cc904d137be2e1730235f5664094b831186.
How do I get my UDID?
You can copy/paste your UDID from iTunes or email it directly from your device by using a free app from the App Store.
Email Using the Free App
Install and run Ad Hoc Helper. It will create an email with your UDID.
Copy/Paste from iTunes
1) Launch iTunes and connect your iPhone.
2) In the right pane, locate the information about your iPhone, including its name, capacity, software version, serial number, and phone number.
3) Reveal the Identifier by clicking on Serial Number:.
4) Copy the Identifier to your clipboard by choosing Edit → Copy.
5) The UDID should me in your clipboard. Now you can paste it in any program.