I would like to suggest a service that would not be all that expensive to impliment, but would solve a lot of the problems subscribers have. It would be a white/grey/black list for incoming phones.
The white list would be anyone on your contact list. Incoming phone calls from this list go right to your phone, and, after a certain time, to your voice mail. This is the normal procedure.
The black list would be anyone you put on it that you want totally blocked. They get an announcement that they have been blocked, but nothing else. This list is normal for blocked calls.
The grey list would be anyone not on your contacts or block list. They simply go immediately to voice mail.The phone is not rung. If they decline to leave voice mail, you never even know they called, unless you check the call log.
This would eliminate, almost entirely, telemarketer calls, since they virtually never leave voice mail. Your important calls still get through.