Back in May of this year Rovio announced that they were going to release a feature called 'Accounts' which you basically let you log into your Angry Birds game and continue playing it regardless of what device you're on. This means that when you get a new phone and reinstall Angry Birds, you won't have to start all over again.
Instead you will be able to pick up where you left off when you were playing on your old Android phone or tablet. Essentially this is a game sync service so your game will be synced across all your Android devices you have connected with your Angry Birds games. Since this is account-based, that means if your friends or whomever wants to play their game on your phone, they can do so by logging into it and it will load up where they left off instead.
As of right now there are only two games with this feature, the original Angry Birds and The Croods. Rovio is planning to add this feature to all their games so expect the Accounts feature to show up soon in other titles.