I found this thread on xda-developers. If you have jail broken iPhone and rooted Android phone, you can transfer your progress.
Basically you have to copy two files, highscores.lua and settings.lua from /private/var/mobile/Applications/(very long string)/Documents from iPhone and replace them on Android phone in /data/data/com.rovio.angrybirds/files/. You also have to fix permission and make sure you've completed at least 1 level in Android phone before replacing the two files.
If you trust yourself you can also use programs like Angry birds unlock all level in Android and unlock only up to the level you've completed in iPhone. But you won't have exact score and hidden star collections. So though little troublesome the earlier way might be what you want.