Call Blocking in android

Hi,
I want to develop an application which blocks incoming calls (Call Blocker) in Android.There were Android internal API for that but those are removed from 1.0 onwards SDKs.We can catch incoming call event using "PhoneStateListener" class,when phone state goes to ringing.

Right now we implemented call blocking using an illusion kind of thing.When we get incoming call event in "PhoneStateListener" event,we switch a phone in AIRPLANE_MODE and again switch off that mode.But behaviour of "PhoneStateListener" is not predictable and blocking in this way is not proper blocking.

There is RIL(Radio Interface Layer) and baseband architecture behind the android telephony api.But how can we send a message to RIL for blocking a call. Is there any API/logic for blocking a call which we can implement using android NDK? OR is there any private/internal framework/API which we can use to block the calls?

Thanks,
mayur