I am doing some search concerning the smartphone's operating systems: Symbian, Windows Mobile, Palm OS...
I have found the answers to almost all the questions I had. They were mainly concerning messaging and phone/SIM interraction and OS general questions.
1 - Is there a way to send/receive "quietly" (without user notification: noise/text) SMS in Symbian C++?
There seems to be no problem for sending "quietly" SMS.
For receiving, from what I have read (I was not able to test it) There is always a noise notification. And if the application is not launched a "reconizer" (correct me if I used the wrong term) is needed to launch the application on the reception of a SMS
2 - Interraction with the SIM card: directly sending commands to the SIM (like client/server application) or simply sending APDU in Symbian C++
It seems that this is impossible to do it using the standards library. it may be possible using the one reserved to licencees.
3 - Differencing the different OS: Is there a way to see which OS (Symbian, Windows Mobile, Palm OS...) is running on a phone?
It seems to be possible when knowing the look and feel of each OS? or maybe by seeing distinguishing drawings: for example on Windows Mobile phones there is always the Windows logo.