J2ME consists of two elements -- configurations and profiles.

Configurations provide a set of libraries and a virtual machine for a category of wireless device. There are two configurations for J2ME, one for fixed wireless devices and one for mobile wireless devices.

Profiles are APIs built on top of configurations to provide a runtime environment for a specific device, such as a PDA, cellphone, or set-top box. The profile manages the application, user interface, networking and I/O.

In order to support Java apps, manufacturers need to implement a profile for their specific devices.

Network Programming With J2ME Wireless Devices 
Sun's J2ME offers a great development platform for developing applications for the embedded electronics and mobile devices.

What's J2ME?
Explains Sun's J2ME download and profiles the development of a PALM OS device application.