The guys behind Angry Birds for Android decided to include a small easter egg / trick that unlocked all the locked worlds.
I’ve completed the game on my iPhone so I decided to give this a try and it worked like a charm!!
Here’s how you unlock all worlds.
1. Launch Angry Birds and go to the world select screen.
2. Select a locked world on the screen. ( The one with a pad-lock )
3. Hit back button all the way out of Angry Birds.
4. Launch Angry Birds again and when the “Play” button appears, keep taping it till you get into your locked world.
5. If step 4 worked, you should now be inside the locked worlds stage select screen.
6. REMEMBER!! To keep it unlocked just pass the first world level of each locked world.