Since this thread appeared, I contacted Matt Herron about phone apps. Getting the feeling it's not going to happen.
However, I downloaded the Appventive Weight + Balance app for Android and it works well. Will contact the developer with a couple of questions, primarily wanting to increase resolution an order of magnitude.
It's $10, and can be with you when you're adding a passenger, water ballast, etc. I move the fuel tanks, rename them and use weight as the input for water ballast.
Will also try Matt's SeeG program. The Jonker Sailplanes spreadsheet for the JS1 is the best I've used so far, wish all manufacturers had something like that to download. But spreadsheets aren't great on a smart phone.
Jim