An interesting feature would be to send class0 SMS (or flash SMS)
With recent phones, the phone displays the text as a pop-up, without saving it nor showing the sender. On older phones the message is showed normally.
This is how it look on the iphone:
http://img709.imageshack.us/img709/9259/imagedc.jpg

It also works on N900 (A member showed a screenshot of a received message and it is displayed on pop-up too, I don't have that post)

The question is does the telephony stack on N900 allow to send class0 sms without heavily hack it ?

Edit: found the thread, it seem that the N900 displays sender and date:
http://talk.maemo.org/showthread.php?t=52963