title: Check to see if telephone number is active/real
body: <p>I have a new project on hand on which is quite complex as i am not aware of its domain.
  My requirement is this, We have list of telephone numbers and from this list i need to check which telephone number is active/real.</p>
  
  <p>How would you program a telephony or IVR system to automatically dial phone numbers on this list and automatically detect if it is a valid phone number or not? I would like to use C# to program this solution.</p>