No no...you cannot challenge a Windows Phone.
A Windows Phone challenges you.


Meaning, they make the rules and choose the prize. But they get no compensation if they win (besides bragging rights and maybe a sale). Besides they try to nulify any advantage you may already have by getting you to connect to the same (slow ?) wifi internet connection and make you restart your phone. Yet they gain an advantage with a phone that's prepared for the specific challenge.

Challenges so far include:
-Change your Status on multiple social networks (Facebook and Twitter)
-See the weather for two different cities
-Take a photo and upload it to a social network (Facebook)
-Take a photo and send it as MMS (they only choose this for competitors with slow cameras)
-Search for the name of a song (eg Shazam)
-There's a lot more which are actually biased towards WP7's built-in features (like Bing search)

They are mostly targeting iPhones because the owners don't have widgets or the necessary Apps.
Also targeting people with old phones (WM6, Palm), featurephones (Symbian) as well as BlackBerry.
They usually smoke Android too, but against people with the prior-setup. They've been shown time and time again that Android smokes WP7.5 in all the challenges if the user actually sets the task up.

If Android can do it, I don't see how the N900 cannot. Then again N900 lacks many features from Android like Shazam support and the plethora of 3rd party Apps. Good Luck !