The implementation package should not be used by developers, it is an internal implementation detail which will break compatibility between major LWUIT releases. The purpose of this package is to provide ISVs, vendors and operators with the ability to customize & enhance LWUIT from within without breaking compatability with existing LWUIT applications.
A vendor extension begins by extending the LWUITImplementation class and implementing the abstract methods within. To use this version of the implementation a user can use the Display class and link to a vendor JAR that doesn't include any portion of LWUIT.