Yes, I am thinking develop the J2ME application with limited modification and run on almost every mobile phones. Just wonder if iphone really support any kind of j2me/j2se program. Then programmer's life will be much easier.
There has been some confusion, so I will state again:
There is NO java on the iPhone. No BREW, no j2me, no j2se, none. There is no JVM, and the likelihood of there ever being one can only be based on whether you believe Sun or Apple.
Since Apple has a pretty firm grip on the official platform, I am betting on Apple's past remarks holding true. As such, I don't believe there will ever be Java on the iPhone.
If there was it would make the *Java* programmer's life much easier. HTML/Javascript and Objective-C/Cocoa are not more difficult than Java, but if Java is all you know and you don't wish to learn anything else, then you are in a tough spot in terms of iPhone development.
I don't think this needs to be as contentious as it has become. Java is a valid language, as is Objective-C. The Java community is larger at the moment, but NeXTSTEP and Apple have championed Objective-C and the iPhone is Apple's baby.
Should it be "open"? That's another thread (and probably forum) entirely, and there is a community dedicated to unlocking the iPhone so you can run whatever you want on it. To access the hardware you still have to use Objective-C to make the calls, but using a jailbroken (etc.) phone, you could write bridges for other languages and program in them.
If you did choose to port a current Java program to Objective-C you could probably easily have it running on full OS X as well as the iPhone and iPod Touch. This may be of no interest whatsoever, but it might be a positive side effect.
-Lee