We have to develop a chat client for mobile. The devices should be for the following:
Android iPhone Blackberry Symbian Windows mobile Windows CE Palm
Which technology we should use for the multiple OS computability. We like the most of code common. This chat client also support the video and audio chat.
Android and BlackBerry: Java Symbian and Win Mo: C++ iPhone and Palm: Objective C and C
It is possible from to write the apps so that some common functionality can be reused, but it needs careful design. But you are a bit out of luck on this.
I would recommend starting with Java and Objective C implementations as this will get you Android, BlackBerry and iPhone, which have a lot more traction in market than other platforms.
Look at cross platform frameworks like PhoneGap - that way you can keep the UI and as much code as you care to port to JavaScript common, then do the remaining in native code.