The update is free for anyone who has an existing copy of Office Mobile, which should cover most Windows Mobile users. it adds support for Office 2007 documents including DOCX, XLSX and PPTX files. There's also enhanced viewing capabilities for Excel Mobile, the ability to add SmartArt in PowerPoint Mobile. Users can also view and extract files from ZIP folders.
If you don't have a previous version of Office Mobile, you can buy a full version of Office Mobile 6.1.