Microsoft today inadvertently previewed its next mobile OS through a preview of Office Mobile 2010. Point 5 in a description of the beta shows a screenshot of the productivity suite running in an environment clearly unrelated to Windows Mobile 6.5 and which is consistent with earlier shots that point to a more touchscreen-friendly interface. At the same time, it retains the familiar two-button options at the bottom of the screen and generates touch lists not unlike the current platform….