Briitsh Gas have an iPhone app. They told me so in a press ad. It will show how my consumption has changed year on year, quarter by quarter.
That's interesting information, but I don't need an app for it. I can see it on my provider's bill already - at a time when I'm more likely to be thinking about the issue and where they already have my attention.
Just because you can have an app, it doesn't mean you need one or that your customers' experience will be enhanced by having one.