CalendarBudget is, unfortunately, not built on the Google API. Its designed to have a similar look and feel so you don’t need to learn a new interface. In fact, we think our mouseover interface is an improvement over Google’s calendar, but that’s another story. :)
We have investigating integrating with a text messaging gateway, however we decided against it for the moment, with plans to revisit this in the near future.
We do have, near the top of my priority list, a mobile app planned. We’ll probably start with Blackberry (rather than iPhone), simply because the Java platform is more familiar. We have a number of small house-keeping items to clean up before we get there, but we hope to have at least a start on it by the end of the year.