It's similar to enhanced lockscreen, but I had to watch some more dbus messages (com.nokia.csd.Call::Coming for the calls as it seems to be fired before the MCE_CALL_STATE_SIG and com.nokia.system_ui.signal::alarm_dialog_status for the alarm dialog).

I don't have any issue with incoming calls and alarm, but some users reported to have some problem (but I don't know what hack/app/mod can cause problems)