This guy has it figured out.
The next big thing will be apps as a service. Buy or rent an app you need for a short time then do it again in 3 days or 3 months or a year when you need it again. This is already available on the general web from your PC and the phone version will follow. J2ME apps run on a variety of devices, although not always exactly the same (different screen specs and I/O issues). And certainly as we move to more SaaS offerings where apps run only in a browser, the notion of an app for almost any device able to handle XML, AJAX, JavaScript, etc., would make apps almost universal. This only works if you have reliable, high speed, and fairly low cost data-driven networks, as this stuff requires users to be connected most or all of the time.