Candidate Calling

We had two calls in the last 2 days from a certain Democratic candidate, probably the lowest number of calls in a recent election since campaigns started doing these robo-calls. A friend had something like 5 calls from Republicans - particularly amusing because they are about the most liberal person I can think of.

Who decides who to call, who does the 'call,' and do ANY of these work? I am inclined to believe they work AGAINST the person named in the call.