Steps to Get the UDID of Your iPhone
If you're planning to build an iPhone app either by yourself or through another developer, you must know your UDID. Without the UDID, you cannot test and review the app on your own iPhone.
When a developer builds an iPhone application, s/he will have to submit that application for beta approval by Apple. Without Apple's approval, the developer cannot install the program or application in his/her client's iPhone. In other words, Apple's beta approval is necessary so that the developer's client can review and test the app on their own iPhone. Once the client is satisfied that the app works as planned, it is then submitted for Apples' final approval so that the app can be generally distributed by the App Store.
Each iPhone or iPod Touch has a Unique Device Identifier (UDID), which is nothing more than just a bunch of 40 numbers and letters. The developer needs to register your UDID with Apple so that Apple can approve the developer's application especially for his/her client's iPhone. Here are the simple steps to getting the UDID of your iPhone so that your developer can register it with Apple.
1. Connect your phone to your computer and start iTunes.
2. Click on your phone on the left navigation bar under devices.
3. Under the summary tab, there is a label - Serial Number.
4. Click on the label - it changes to Identifier (UDID). Note that this label looks like nothing more than just text -- it's not highlighted or otherwise marked to indicate that you can click on it.
5. Hit Ctrl C or Cmd C (if on a Mac) since you will not be able to simply select the UDID and copy it.
6. Paste the UDID in your email, notepad, word, etc and save it for future reference or send to your developer.
The UDID will help your developer create an app build that will run on your iPhone or iPod touch. Remember, if your developers needs to have another of your iPhone or iPod touch run the app s/he has developed for you, you will need to follow the steps above to get those devices respective UDID.