Previously Microsoft has released OneNote for iPhone, and iPad other than Windows mobile devices and now OneNote for Android is live on Android Marketplace, and available free for download.
With the free version of OneNote for Android you can access, create and edit up to 500 notes.
To work with OneNote on Android you must sign in with Windows Live ID and its compatible with Android 2.3 or later.
Download OneNote for Android
On the launch event of Office 2010 for business users, Microsoft also has rolled out Office Mobile 2010 for Windows Mobile 6.5 users. This package of Office Mobile 2010 includes the applications as Microsoft Word, Excel, PowerPoint, OneNote and SharePoint Workspace.
According to Microsoft this latest version of Office Mobile 2010 gives enhanced functionality for touch screen devices and increase user experience to work with Office apps on mobile devices more efficiently.
So, if you have Windows Mobile 6.5 then you may download free Office Mobile 2010 through Windows Phone Marketplace.