While there are some 3D physics engines for J2ME, there is none for 2D. In these days 3D games still have big problems on mobiles phones and burning the CPU with additional collision calculations is not wise - who wants to play a game running at 3FPS
On the other hand the situation at 2D games is much better. Currently there is plenty of free CPU performance that can be used for 2D physics (which is not so "expensive" as 3D physics). I was surprised when I couldn't find any 2D physics engine for my J2ME mobile games and that's why I created one:)
DyMiX is currently just basic rigid body physics engine with no special features, but it doesn't matter. Mobile games are simple and there is no need for a very sophisticated and complicated engine. As you can (hopefuly) see from the demo.
you can learn more about the engine, download a demo or watch the video from the demo.
Here is the direct link to the video for extremly lazy boys and girls: http://www.n-joy.cz/video/dymix-2d-physics-engine-for-j2me/6PedOkbF4tnBcCiJ/
I hope you like the demo:)