If you're considering developing data management for Java ME, consider the case of Movimiento ATM, an Argentine mobility software company that saved time and money by swapping its "homegrown" database for an off-the-shelf Java ME DBMS.

http://www.jroller.com/perst/entry/h1_movimiento_atm_perst_lite 

Perst Lite is an open source, object-oriented database management system (DBMS) for Java ME.