J2ME is the only environment to develop something on mobile devices, but unfortunately sun kept it too limited to avoid any security issues.
On the other side Symbian is much more open, but unfortunately it seems like it’s too complex to be interesting to most companies. I certainly wish OEM’s will eventually move to open systems. Linux embedded would actually seem to me like the easiest choice. LiMo foundation seems like a step in that direction, let’s see if it’s just another initiative or something that turns into reality ( http://trasatti.blogspot.com/2007/02/limo-foundation-launched.html )