Sorry folks about the delay, but my son's birth made me stop all working and hobby threads
I finished a version but it was to big for my siemens S55 JVM take care. I got a "OutOfMemory" exception on face.
I will need to make a clearing on adapted code for a better image generation and ROM load.
I'll send news ASAP.

hehehe, you say it the right way: made me stop.... for 'crying' out loud!!!!!!!

NEWS. It worked on Sun SMTK, but it was tooooo slowwww. But I got a happy moment besides it took 5 minutes to start up the ROM BIOS and more several minutes to go to BASIC interpreter shell. (On a Sony VAIO P4 2.8Ghz)
I optimized the drawing, but its not good yet.
The instruction dictionary must be optimized, but i dont know how.
May be switch case doesnt work well in J2ME. And it is using MIDP 1.0 API. Does exist Game Graphics classes like MIDP 2 in MIDP 1?I guess there is a specialized way of drawing bits in Siemens Mobiles. I will search a way out.

I think actual (common) phones are not fast enough for running a j2me MSX emulator. Moreover, they have a limited heap memory, JAR restrictions, etc. which means it is a hell to try it. Furthermore, MIDP 1.0 is quite limited with graphics; you can't have pixels access and the only available methods are drawing (copying) images, drawing primitives (lines, rectangles...) and a few more.
You can try to focus the emulator in a concrete model or family like Nokia S40, S60 in order to get some special API's for sound and graphics. But I think it will not be enough for doing a decent MSX emulator.

Besides I got a S60 model (nokia 7650), I still interested in developing a pure J2ME emulator. It worked here, but too slow. No sound and a horrible sprite drawing routine, but it did work (I saw Konami´s Nemesis on screen). Im trying to imagine a way to optimize the Zilog Z80 CPU emulation. The original decompiled is a "big switch" in the 256 instructions. Im working in make a more inteligent instruction match using a statistical approuch or a way of grouping instructions in sub sets for a kinda of hash matche. Any ideias?

Did you try to run profiling on the code ? If yes, was the mentioned code section identified as a bottleneck ?

If you have a S60 phone, why not use the wonderful fMSX/S60 emulator?

Why not fMSX?
J2ME can be spread around any J2ME device. Symbian rocks, but I love challenge. In future, it can grow to a sofisticated emulation in JAVA. Sun will love this.

About CAS question, I used System.getCurrentTimeMillis(), I will try to use the profilling tool to confirm the bottleneck.
The worse bottleneck is not in Graphics, but in CPU. It takes minutes to start VDP.
I boosted the code just with bit operations to multiply and div some values, but it far from a good emulation.

I will try other optimizations techniques.

Does the object code (the classes) differ in various compilers? Maybe you need some more sophisticated compiler, which uses many optimisation techniques.

Maybe we should all code JAVA in bytecode

This post is already old and I believe lots of people here have already ported Arnon's J2SE MSX emulator in J2ME. But if not then just try mine:

http://genergabasa.php0h.com/upload.php

Also, on that page are other java emulators ported to J2ME.

Enjoy!!