I want to delete Angry Birds from my phone, but keep my score and state, so that if i install it again later, and sign in, it will preserve my current achievements. Is that possible?
On iOS, the actual GameCenter achievements are stored on Apple's servers. You don't need to back them up. The progress is saved in
On Android there are no achievements but for backing up progress, there's an app for that. If you have root, you can also manually back up
I would expect similar options to be available for other platforms. (See How can I move my progress from one machine to another on Chrome Angry Birds? as well).