There is a new article up on GameDev.net Start to Finish: Publishing a Commercial iPhone Game. In the article the author says he was going to work in J2ME but said that it was limited to a single key press at a time. Is this true?
The API isn’t - key events are handled in a similar way to J2SE/AWT.
However, some devices are restricted at the hardware level to only track a single key at a time.
Thanks.
Kinda late but I just saw this topic.
On some mobiles you can fake it.
As Abuse mentioned, you will get keypresses and keyreleases. Some (iirc) also offer keyrepeats.
So by just tracking the keypresses and keyreleases, you could fake such a system.
The only problem is, some devices have problems with pressing multiple keys.
Say you press 5 and get a keypress. Then press 6 and again get a keypress. Release 5 … no keyrelease. 
So you could also just fake releasing the key if you knew which key was pressed before.
MIDP2.0 offers some features that make life a little easier, but then you are restricting yourself (fine for private projects).
HTH