Just like the saying "How long is a piece of string" nobody can say with any degree of certainty how many calls it will take to any individual or organisation in order to make a calling campaign successful. 

We all have to start somewhere. The good news and the bad news is this: The greater the number of calls you make, the more effectively you separate yourself from the crowd. The "crowd" in this case will be anyone and everyone that has given up on ever speaking to someone after one, two or three calls.