I would like to develop a new input method like T9, Letterwise, iTap, Suretype and so on. I want it to work on simple candybar phones. It's likely that I can make it on the most recent versions of Symbian, but I'm going to buy a cheap Nokia, maybe an old one. What is the oldest/simplest OS on which this is makeable? Will I be able to load my program on any mobiles using this OS?
I'm asking because it's not a typical external application. Perhaps it needs a deep access to the OS that only a few versions of Symbian or S-whatever can provide. Besides, I want to display a virtual keyboard on the screen when the user is typing.
By the way, do you know any serious Nokia-based projects such like this?