J2ME (Java 2 Micro Edition) is a scaled-down version of the Java platform that is available on most mobiles phone and many PDAs (Palm, Windows Mobile, Blackberry).
J2ME is commonly used to develop mobile phone games. The game developer gets complete control over the user interface, and the developer may also use J2ME's mobile data capabilities to transmit data over GPRS and 3G.
Since J2ME technology is already prevalent, why not use it for your enterprise applications? Your user interface can't possibly be more complex than a mobile game. If you require backend data processing, just transmit the data via GPRS or 3G to your servers.
Talk to your favourite Systems Integrator and explore the possibilities of mobilising your enterprise applications through J2ME. Be sure to discuss the security issues too.