Interestingly, a Wise One on another forum has suggested
Android or
iOS as possible development platforms (although it must be said that he is into games).
There again, there is always the
BlackBerry OS. Or
Symbian*. And Windows
Mobile or
CE. Some of that stuff seems pretty "open" (with SDK's available,
etc.), whilst others appear to be a bit, umm, "closed". So that's
them kicked into touch, then!

The Android operating system consists of 12 million lines of code including 3 million lines of XML, 2.8 million lines of C, 2.1 million lines of Java, and 1.75 million lines of C++.
Yes, what a mess! But probably more lines of code than the program "running" (plodding?) the
www.police.uk website, then!

To my mind, if anyone is planning to put in time and effort in developing applications for hand-held devices, then s/he needs to be sure that the fruits of all that labour will end up working on as many platforms (devices) as possible. I can't help but wonder if good old DOS isn't in fact the answer (oh, titter ye not). That is, develop in DOS, and then run the app(s) on whatever hardware-software combinations ("platforms") support DOS emulators (and I'm hoping that many - or even most - do). Hey, it could be a chance (excuse?) to take another look at my old DOS stuff!
AndroidBlackBerryiOSPalmSymbainWindows*
The successor to Psion, in case anyone was wondering (and therefore very "worthy", in my opinion)!