I'd have to recommend c++. I own an iPhone myself, so they are definitely fun, but c++ is more ubiquitous. Personally I know C far better than c++ (which is a superset of C). The main difference is c++ has classes and more "object oriented" concepts. For the long-haul c++ I think will have more staying power than the iPhone - who knows, maybe the iPhone will be not as popular in a few years, but c++ will still be here.