In MIDP if you want to run a Midlet in the background (that is, not have it affect the display or command listeners), you call display.setCurrent (null). This was not implemented in any of Nokia's MIDP 1.0 phones (why I do not know).
This is a HUGE problem with MIDP 2.0 though, because of the Push Registry. The push registry let's you call a timer based Midlet (like to have your phone sync with your PC every 5 minutes). The LAST thing you want to have happen is to interrupt the user's display every time the timer goes off.
In emulation, however, using the emulator contained in Nokia's MIDP 2.0 developer' Suite, that is exactly what happens. PLEASE tell me this will NOT be the case for the 6600. Nokia? Will you tell me this?