Maemo/Meego community has been working to fulfil the wish of many N9 users to have 3rd party application Whatsapp on their phones. The Meego version of this application has not been released by the parent company even after many petitions and requests from N9 users on many forums.
But now thanks to the vibrant Maemo community, ported Whatsapp application for your N9 and N900 devices will soon see light of the day. The developement is rapid and thanks to some posts in Maemo forum, it seems beta can be released next week.
Below is a snapshot of the ported application on N9, which is considered to be in alpha stage now 
i guess this is where the whatsapp guys failed it, why can’t you just make it for nokia N900…
sadess phone ever….nokia n900
whats app for nokia n900
Whatsapp
whyyyyyyy whats app is not available for nokia n900?????
The n900 HAS BEEN THE WORST PHONE PRCHASE FOR ME EVER. G TALK WORKS NOT. NO WHATSSAPP… CRAP!
Pliz guys its now October waiting is whatsapp for nokia n900 still coming out. Pliz respond on leeroypike@gmail.com
No news from the developer. Seems it has been abandoned.
have downloaded whats app bt when i enter my cell no. and imei no. with sms after verify it says Unknown Error :::: please help me out here for Nokia N900 ….. my email id himanshu.spykar@gmail.com
if u founded send me pls :skyminab@yahoo.com