Block aggressive advertising calls

In my country, but I bet anywhere else do the same, the telephone calls for proposing new products are constantly increasing, these annoying calls, sometimes malicious, aren't always welcome.

My country has adopted a kind of institutional way to handle this phenomena, it is called  "registro pubblico delle opposizioni", using this, any citizen may publish his telephone number, merely this action should him guarantee he would never ever receive again any advertisement call.

Unfortunately, reality can't be more distant from what really is going to happen.

Telephone spammers do not use to follow rules, and the weak statement "this user does not want to be called for commercial purposes "  is not enough to prevent they to call you. 

If you do not want to be called, you have to find yourself a way to do that.
In other words, you have to find a way to recognize them as spammer, and forward them, for example, to an announce stating you do not want to be called.

As an Asterisk user I have a framework at my disposal, which potentially lets me route calls using any sort of policy; but the main issue is how to identify a spammer?

Internet community, seems to have faced this problem and has built a kind of database in which people complaints about telephone numbers.

It exists, for example, a service called TELLOWS on which anyone can leave a comment on a source telephone number.

So why don't use those information to identify spammers and avoid unwanted telephone calls?

My proposal is integrate the service provided by TELLOWS in the Asterisk dialplan.

Here an example of my thougths.

in the Asterisk dialplan

exten =>  incoming,       1,              Noop(Incoming call is just arrived)
exten =>  incoming,       n,              Set(tellowsc=${SHELL(tellows_c.sh ${CALLERID(num)})})
exten =>  incoming,       n,              GotoIf($[${tellowsc}>1]?reject)
exten =>  incoming,       n,              Dial(${destination},30,${FLAGS})
exten =>  incoming,       n,              HangUP()
exten =>  incoming,       n(reject),      Answer()
exten =>  incoming,       n,              Wait(2)
exten =>  incoming,       n,              Set(CDR(userfield)=RejectedByPolicy)
exten =>  incoming,       n,              Playback(spam)
exten =>  incoming,       n,              HangUP()

the bash script for the italian version of TELLOWS

#!/bin/sh
score=$(wget -O - -q "http://www.tellows.it/num/$1" | grep "/images/score/score[0-9].png" | grep scoreimage | sed -r 's/.*score([0-9])\.png.*/\1/');
comments=$(wget -O - -q "http://www.tellows.it/num/$1" | grep "itemprop" | grep "Numero di commenti:"| sed -r 's/.*>([0-9]+)<.*/\1/');
echo -n "$comments";

I used, to reject calls, the number of comments the number has, but there's also a kind of number score, you can use to take your decision