Sun has open sourced various parts of Java under a GPL 2 license. Included within this is a build-able version of Sun's Java ME implementation. Also open sourced is the Java ME testing and compatibility framework. Sun are hoping to speed up the development and evolution of the Java platform and say that open sourcing the language will help drive down development costs and reduce fragmentation.

The implications of the open sourcing of Java ME for end users is minor. Both Nokia and Sony Ericsson have their own implementation of Java ME and are likely to continue to develop these. However it is possible in time that they may use parts of the open source project.

Similarly for most mobile developers little will change immediately. For those who work in Java across multiple platforms or those involved in the creation of run time environments then it is likely that this will begin to have an impact. The release of new versions under open source will clearly have an impact.

However in the longer term such a move is healthy for Java as a whole because it moves it away from control by a single corporation. This will make it more attractive to developing countries such as China and Brazil. Moreover it also allows greater community input into its direction. 

See also:

Sun open sources Java ME under GPL [Forum Nokia Blogs]

One giant leap, two small steps [Mark Reinhold's Blog]