Each iPhone has a unique device identifier (UDID) number that stays with it no matter what happens. In fact, I discovered that if you sell your iPhone and have it covered under AppleCare, that UDID number can be used by the new owner to get it repaired by Apple. Very cool.
On the other hand, some developers use your UDID to associate it with user information for their application. That means if you sell or give your iPhone to someone else all your account information may be accessed by the new owner. Not cool.
So, why the boot camp on UDID?
Apple devised a new system for the launch of the Push Notification service to identify your unique iPhone. It's called a device token. Unlike the UDID, it can change from time to time and it is seemingly causing all sorts of problems for Push Notifications.
According to Apple, in certain "edge cases" the device ID token may change when you sync with your computer. If that happens, you won't be receiving any more Push Notifications because the services that push you messages don't know it has changed.
In addition, this is why some people who tried to activate their phones without using iTunes are having problems with Push Notifications. When you bypass Apple's activation process a device token isn't created for your device. Thus there's no way for Apple or the developer to push you an alert.
Not only that, but AIM has been sending some random Push Notifications to people. The theory as to why this is happening is because someone is trying to hack the unique tokens so "hacktivated" (iPhones which were activated outside of iTunes) users can benefit from Push Notifications. But it isn't working correctly. Two or more people might be getting the same device tokens and receiving other people's messages.
Our resident wizard on these matters says it would be a good idea for every iPhone user to make it a habit to relaunch every app which uses Push Notifications after you sync with your computer. When you launch an app that uses Push Notifications the iPhone sends your unique token to the app's servers. So if you're missing Push Notifications, the token on that app's server may be an old one.
Opening the app may be all that's required to fix.
