Feature request -- SMS spam blocking?

[Derek Pressnall]

Question about how SMS messages work.  Does the software stack have to
perform a a seperate action to retrieve an inbound sms message, or is
the message text actually part of the alert from the gsm chip?  If a
seperate action has to be taken to retrieve the sms message, then do
the phone carriers charge for the message regardless if it is
retrieved?
If the inbound sms alert contains a source phone number, then it would
be a nice option for the messaging app to accept only messages from
people in your address book (ie., whitelisting).  Could be an
effective way to block sms spams.