For PL4, if you can get (legally) the "Angry Birds" package for Palm Pre or Android with all the 1.4.2 levels, you can decompress it and copy the "levels" directory content into "/opt/rovio/angrybirds/data/levels".
After this manipulation, I get all the levels including PL4 in my N900 "Angry Birds" version .
am i the only one who dislike it that android users are getting lvl pack 1-3 for free and we have to pay for it?
Last thing N900 users should be complaining is available games for N900 especially from developers like Rovio. I mean largest mobile game is available for platform that's fraction of ios and Android.
Rovio has made game for N900 that no other platform got and that's free and no ads, bounce.
Angry Birds does not even run on all Android devices and Rovio has been very vocal about the fragmentation of Android. Though working nicely on Galaxy S.