Google has released an update to the mobile version of its Google Docs website which adds the ability to do some editing to spreadsheets, not just view them.
While not yet a full spreadsheet solution, Google Docs does now allow users to add new rows, edit existing cells, sort by columns, and filter by terms.
Good for Android, iPhone, and S60... and Maybe Windows Mobile
This new feature is only usable on mobile devices which use a browser that is powered by the WebKit rendering engine, which includes Apple's Safari Mobile, the Nokia S60 Browser, and the Android browser.
In addition, third-party browsers for Windows Mobile such as Iris and Torch Mobile may also be able to perform these Google Document spreadsheet edits.
To check out these new capabilities, visit m.google.com/docs from a supported mobile browser.
Naturally, this is a free service.