New to Mobile App Development

Hi all -

I have been out of touch with programming for about 4 years (started my professional career as a J2EE developer, but moved to the business side of things thereafter).

I am looking to develop a mobile phone application which will:
1) not require internet connectivity for running (other than an initial download).
2) be used to generate passwords (so it might involve some intensive computations, but nothing too heavy).
3) will not be UI intensive (will only generate and display passwords).

I want to develop this app for use on regular/cheaper java-enabled mobile phones, windows devices and blackberries (not iPhones yet).

What software should I develop this app in in terms of efficiency, compatibility and ease of deployment across various mobile phone operating systems?

Thank you!
Tarun