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:
Why do we need the UDID?
Your iPhone can only install programs that are approved by Apple. Applications in the App Store have been approved by Apple for general distribution, but beta customers get to try the app before it’s in the store. We register your UDID with Apple so they can approve our application especially for your iPhone.
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 (iTune)
Copy/Paste from iTunes
- Launch iTunes and connect your iPhone.
- In the right pane, locate the information about your iPhone, including its name, capacity, software version, serial number, and phone number.
- Reveal the Identifier by clicking on Serial Number:.
- Copy the Identifier to your clipboard by choosing Edit → Copy.
- Paste the Identifier into an email to email@example.com (You should be able to paste into your mail program or web browser by selecting Edit → Paste).
Reference : Here
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