In my app I will maintain a list of contacts.
Any calls from contacts in the list will be dropped. They will show under missed calls but the phone will not ring.>
Download the class of ITelephony from here.
Then put it in a package (make a new package) of com.android.internal.telephony. Then import the package to the appropriate class and for rejecting a call use the endCall() method
com.android.internal.telephony.
endCall()