ON LINE Mobile Development:

This page lists the known relative differences between the most popular mobile platform development options for handheld devices such as personal digital assistants, enterprise digital assistants or mobile phones. It is not intended to be an absolute guide to the various mobile development platforms; instead it is to help guide developers in choosing a mobile platform for development on Information appliances. More detail on the subject can be found at the Mobile software article.
JAVA ME:
Ideal for a portable solution, if the Java ME platform provides the needed functionality. Good for vertical applications that must be portable. Device-specific libraries exist for many devices and are commonly used for games, making them non-portable. Applications (including their data) cannot be larger than around 1 MB if they are to run on most phones. They must also be cryptographically signed in order to effectively use many APIs such as the file system access API. This is relatively expensive and is rarely done, even for commercial applications.
Symbian:
Very powerful for general purpose development. The Simian based S60 platform is strongly supported by Nokia with some support from other device manufacturers. In Japan NTT DoCoMo's Symbian based MOAP platform is also well supported by a number of manufacturers (Fujitsu, Sony Ericsson Japan, Mitsubishi and Sharp amongst others). It should be noted, however, that MOAP is not an open development platform. Another Simian based platform, UIQ, is less well supported (principally by Sony Ericsson and Motorola). Currently large device deployments in Europe and Japan, with little penetration in the US market.
Iphone:
The iPhone and iPod Touch SDK uses Objective C, based on the C programming language. Currently, is only available on Mac OS X 10.5 and is the only way to write an iPhone application. All applications must be cleared by Apple before being hosted on the AppStore, the sole distribution channel for iPhone and iPod touch applications. However, non-Apple approved applications can be released to for jail broken iPhones via Cydia or Installer.