This post talks about Office Mobile 2010 Beta; Basically, there’re two major offerings provide for mobile information workers to work on their Office documents. Depending on type of phone you’ve, you get to choose best that work for you. One is Office Mobile 2010 and another Office 2010 Mobile Viewers. In short:
…If you’re using a Windows Phone
You get both options. If you want to modify your Office documents, you can use Office Mobile 2010 applications providing rich user experience which customers of Microsoft Office client applications’re familiar with. If you just want to quickly view documents, you can use Office 2010 Mobile Viewers which display your documents in mobile IE browser.
…If you're using a phone built on a non-Windows Platform
You get Office 2010 Mobile Viewers option only. As previously mentioned, you get to view Office documents in your mobile browser whether you’ve smartphones like iPhone, Blackberry, Android, Symbians or non-smartphones.
Full Article: Office 2010 blog