Each iPad, 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.
To find your UDID:
1. Launch iTunes on your computer and connect your iPhone or iPad via USB cable.
2. In the right panel, locate the information about your iPhone or iPad, 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. Paste the Identifier into an email to firstname.lastname@example.org (You should be able to paste into your mail program or web browser by selecting Edit → Paste).