I wanted to help, but sorry to say that i could not understand you fully.
1,You want the app to start and stop processes?Threads - not processes if i am not wrong.
2,Even on exit the app should run in the background?Some phones(eg Series 60 3rd edition onwards) supports multitasking. Which means you can hide your midlet UI, meanwhile your threads can still execute.
(My boss is a Jewish carpenter)