I've been getting these call for several years.
This what I've found to be pretty effective.
I made a list of spam callers phone numbers and when one of them call, I answer with
AN INDIAN ACCENT AND SAY HELLO, HELLO, HELLO, AND I DO NOT IN GAGE IN CONVERSATION WITH THEM. This drives them crazy and they hang up.
Mission accomplished! Then they put me on their DO NOT CALL LIST. !!!! I win.  

Now, those call have dropped off a lot.
It works for me, Try it You'll like the results.
9/6/13

calls sevral days in a row 2x a day w no answer, busy signal on other side.

Call me 4 times a day! No answer!

Recevied call from this number and nobody was on the other end.  I read that this is the CA Nurse Organization calling so I called their Oakland Office and let them know that calling and hanging up is just ridiculous.  We've got to put a stop to the automatic robo-calling systems.  Can someone please write a proposition for the ballot.  Let's require that anytime someone calls your phone that a live person is on the other end.

Same here. Several calls, no voicemail message. And when I call back, I get a busy signal. Landline carrier is CF COMMUNICATIONS, LLC DBA TELEKENEX - CA

This person just called me, male, and asked for me in another language, then hung up. when I called back, the line was busy for a long time.

Hey Leland Yee or Ed Lee, if this number is yours. You better stop calling because you won't get my vote. P**sY.

This number has been calling me for 4 x. Pickup the phone and the other party hang up the phone. When I called back, the line either keep on ringing or busy tone.

I answered a call from this number and it was from the CA Nurses Association telling me to vote for Leland Yee. They were extremely pushy, could not tell me what propositions Leland Yee was endorsing, and specifically asked that I not vote for Mayor Ed Lee (citing the voter fraud issue).

Just ignore this number. I wish I had.

I've been getting calls from this number for days. No one's ever on the other end, and when I call back it's a busy signal.

Have received at least five calls from this number. There is never anyone on the line and they don't leave messages. I tried calling them back but they do not pick up.

I've gotten two calls from this person in three days.  Answer and he/she says nothing.

It was a political call for the mayoral election 2011

Me too - a call on 10/29/2011, 12:36pm PST. When I answered they hung up.

Received a call Oct 29, left no message

Received on October 26, 2011 at 07:34pm and October 29, 2011 at 12:16pm.  I answered, but they hung up.

Received a call from this number 3 days in a row -- did not leave a voicemail.

Called this morning and left no VM. This number called me at least 3 times in the past so I finally decided to call back.... Got a busy signal.

Called again this afternoon

After calling several times without leaving a message, I finally answered.  It's the California Nurses' Association calling with questions about the upcoming election.

Called last night. Left no message. Had called once before as well.

Called through to VM, but did not leave a message.

called and left no MSG last night.

Received a call, did not leave a message.

Just recvd call 6:41pm. Hang up, no one on other end. Called back with no answer

10/24 23:11 Zulu, rang all the way to v-mail, but left no message

10/24 23:11 Zulu, rang all the way to v-mail, but left no message.

no message