Well, While I had been using my N95, I used to have a neat app called "call and sms guard" or somethin like this. The features were,
1. Blacklisted callers or sms senders (Contact Numbers in this list will have their calls cut the moment it reaches your phone and their sms will be deleted without question)
2. Baby List (Contacts in this list will have all their misscalls removed from the phones call logs and moved instantly to another log that is maintained within the application. Same with the Sms)
3. File Encryption.

I think all that will be required is the second point stated above. I know that this is linux based maemo and their are limitations to it. Hope some genius maemo programmer comes up with a whole new source code that will make this device,UNSTOPPABLE :P.