An emulator

There are many emulators available for all the leading phones, and a generic emulator available with the standard wireless tookit available from Sun.

Basically get yourself the standard wtk from Sun and you've got an emulator. Then get the Nokia or Sony Ericsson SDK's and you'll get access to specific emulators for their phones. Motorola, Siemans, samsung and ..well everyone, also have SDK's but they are variable in quality.

Remember that no emulator is 100% effective, they always have some feature wrong or missing its always better to work to your target phone if you can. The Sony Ericssons have a big advantage with their on handset debugging ability too.

Hope this helps

That helps alot thanks :D

I'd recommend mpowerplayer, which is a very owerful and customizable runtime environment for J2ME games. It's also less buggy than your average emulator, and it loads up quicker and does not try to emulate a cell phone (at which most 'real' emulators seriously fail to this day!), but instead provide a decent PC platform for development, software demos and experimentation.

It also includes the necessary libraries to link against, which helps a lot if you are a beginner. The documentation is good and getting mpowerplayer to work for your program is a piece of cake.

Mpowerplayer also provides a platform where you can sell you indie games or demo them to others easily (you can pass them an url to a JNLP file and mpowerplayer takes care of the rest).