Q:

Device Token - Apple push Notification Service

is device token changes each time when i opens my application?
Apple server uses the same device token every time or the new regenerated device token?

A:

You can check developer documentaion, following is mentioned there - 
The form of this phase of token trust ensures that only APNs generates the token which it will later honor, and it can assure itself that a token handed to it by a device is the same token that it previously provisioned for that particular device—and only for that device.
If the user restores backup data to a new device or reinstalls the operating system, the device token changes.
So they are uniques to iPhone until OS is reinstalled.
You can check details here - http://developer.apple.com/library/ios/#documentation/NetworkingInternet/Conceptual/RemoteNotificationsPG/ApplePushService/ApplePushService.html#//apple_ref/doc/uid/TP40008194-CH100-SW12

