|This is far from complete, but lists some major platforms.|
|MIDP||For Java applications running on virtually every mobile device. Most of the content here is about MIDP anyway.|
|Symbian OS||Many mobile devices use this operating system. You can write native applications for them using C/C++ or other languages. Find out more information at the Symbian Homepage. Nokia owns Symbian, but other manufacturer also use this platform.|
|iPhone (and iPod Touch)||
A device with interesting capabilities. Also, it is a single device with a large user base, so writing applications for it is possible without worrying about screen size. It features a motion/tilt sensor which is a nice gimmick. Furthermore, deploying and selling applications is made easy via the Appstore.
However, there are also some serious drawbacks:
The response to the iPhone? This is a rather new java-based platform for smart phones from the "Open Handset Alliance". It also features a marketplace similar to the AppStore. The project seems to be somewhat dominated by Google, and there have already been cases of applications getting banned from the Android market. However, as far as I understand it, there are no constraints on getting applications from other sources.
The development kit looks rather complete at first glance with eclipse integration and debugging + emulation, and it is available for Linux, Windows and Mac. However, I didn't actually build more than a "Hello World" application.