this is my one idea(its in brainstorm please vote)

Call Rejector
a simple call rejector application which rejects calls listed by the user.
1. allow list - when active only calls from the listed numbers will be allowed.
2. reject list - all calls are allowed EXCEPT the ones listed in "reject list"
3. auto reject unknown numbers - numbers not stored in the users contacts are auto rejected. (option to turn this feature off)
4. private numbers - private numbers are auto rejected (option to turn this feature off)

the application will be similar/a replica of HandyBlacklist for the S60 platform.

Future Improvements - SMS/MMS rejection following the same examples/options as above.

Im not a developer but would be keen on going through the process to help with develpment.