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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.

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.

Kevin Junghans
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user867198
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    This sort of information does not come free. In addition calling people without their permission at least in the United States is against the law because of the "DO NOT CALL LIST". Do you have the hardware to automate the process of calling somebody? The information made public by the phone companies when published is accurate. I suggest you contact one of the national phone companies and request information on how to setup a license to harvest their directory. Link: www.donotcall.gov – Security Hound Feb 07 '12 at 12:35
  • @Ramhound this is pretty harsh, -ve rep also given. What if my client has the list which is filtered from your "DO NOT CALL LIST"? – user867198 Feb 07 '12 at 12:40
  • @Ramhound this is pretty harsh, -ve rep also given. What if my client has the list which is filtered from your "DO NOT CALL LIST"? And i dont want any personal info of User, i just want to check if phone number is active or not. Does VoIP helps here or do i need a physical device? – user867198 Feb 07 '12 at 12:42
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    @user867198, I doubt checking to see if a telephone number is "real" is strictly a programming question. If you had an API you were calling, or were showing some code that you've tried then maybe. Just saying "Can I do it via VoIP" does not a programming question make. (Also, you're assuming that Ramhound down-voted you. That could be an incorrect assumption) – Rob Feb 07 '12 at 13:02
  • @user867198 - I gave this question a negative vote because the question is vague. Like I said contact one of the phone companies and request permission to harvest their phone directory. All I know about the subject is that this information is NOT free. I was only telling you about the national do not call registry because you didn't indicate you even knew about it. This type of question "blanket how do I do this" is not a good SO question. – Security Hound Feb 07 '12 at 13:12
  • @user867198 - **Does VoIP helps here or do i need a physical device?**Do you have a dialer? Do you have any sort of phone equipment? Most of your questions could be answered by the phone company. You wanted an automatic way of trying to verify if a phone number is still in service, the phone company can provide this information, the information is of course not free. – Security Hound Feb 07 '12 at 13:15

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Putting aside the legal issues with the "Do Not Call List", the only way to determine if a phone is valid or not is to listen for a Special Information Tones (SIT) that the carrier puts out when the phone is disabled. To automate this you use something called call progress detection or call progress analysis (CPA). You can do this with some IVR systems and the open standard called Call Control XML (CCXML). Voxeo has an IVR platform that has great CPA and you can try it out for free in their hosted environment. Check out their documentation on outbound calling and it will walk you through using CCXML to make outbound calls and detect the SIT tones. One caveat on SIT tones is that some people put anti-soliciting devices on their phones that basically puts out a SIT tone to fool automated systems.

Here is an article that describes how to use an open source project called VoiceModel to develop a proactive notification system in C# and ASP.NET MVC.

Kevin Junghans
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  • I want to ask "WHY" to the question "why are you helping somebody who might be looking to call random people?". Of course the information you provided is actually interesting. I knew there was both a standard and an official process that is used, I just knew nothing about it, besides the fact I am tired of people randomly calling me :-) – Security Hound Feb 07 '12 at 17:10
  • I am trusting that this technology will be used within the letter of the law as defined by the FTC. Whoever does not risks huge fines and penalties. There are beneficial uses for this technology and the industry term is Proactive Notification. For example, I do not mind getting an automated message from the airline that I am using to let me know of a gate change. I also hate misuse of this technology. – Kevin Junghans Feb 07 '12 at 20:21
  • This is a very useful answer and I upvoted it. In my company people provide us with phone numbers. In some cases the numbers are incorrect, either by mistake or on purpose. In either case, we're going to try to call them to respond to their request for info. – Larry K Dec 18 '12 at 10:07