If they write for handhelds, then they'd better stick with Java so that their code is more easily ported to other types of handheld. Perl does not come as standard on *any* handheld I'm aware of. Java does. Perl is not even *available* for some handhelds, which have at least a subset of Java available.
But really for maximum portability *and* minimum footprint, I'd go for C. Yes, the user interface would need rewriting for each platform, and the file access stuff would need rewriting for some platforms, but provided that the code is kept nice and modular, I expect that the core of the application, all the *functionality*, could stay the same.