Every iPhone, iPod, iPad & ATV has a 40 character long Unique Identifier (UDiD) made up of numbers and letters that are specific to that one device. Serial Number is not UDiD.
Device Serial Number
Why do we need your UDiD?
If you want to Develop & Test apps on physical device, device must have its UDiD registered on a Registered Developers Account. Therefore if you want to install iPASTORE and start developing and testing apps, We need your UDiD.
Device UDiD Number (Click Serial Number)
How to find your UDiD
Do not use AppStore applications to find your UDiD, Apple deprecated developer functions related to udid since iOS 6, so they will not give you correct UDiD, Only iTunes or profile checking can get your right UDiD!