From what I have seen, networks seldom use the device IMEI for subscriber identification opting instead for the SIM cards IMSI or an electronic serial number.

Towers though do log traffic using the IMEI... So yes, the N900 should be capable of making "emergency" calls without a SIM and the tower it uses to connect to the system could also record the device IMEI.

I still don't understand this "security POV". Are you asking; when the N900's radios are off and no SIM is inserted will it still transmit its IMEI to the nearest tower?

EDIT: I see that you clarified you question while I was preparing a response.

Also helpful >> http://nds1.nokia.com/files/support/...-US_es-LAM.pdf