Landline number validation - How?


I am currently researching a product which will be able to validate a land line as being in use and live.

The method must not make the phone ring, or cause it to be engaged at all.

I’m aware there are companies that provide this service. If anyone can offer any insight into how this can be done, or how companies are doing it.

Much appreciated.

I hope this is not possible (although there maybe sneaky things you can do with direct access to ISDN protocols).

Generally it is the prelude to an outgoing campaign which is going to annoy tens of thousands of people. You find very few people will give free support for people running outgoing campaigns.

Thanks for the reply. I do understand your stance, as I have just blown in without revealing my company’s identity.

What I can say publicly is that I work for a reputable company who have been running campaigns for a large proportion of the major brands and charities, across voice, SMS and email, for around 10 year - totally by the book.

But yes, if anyone answers my question here, they are putting information in the public domain.

We are investigating a new product similar to this one: … sting.aspx

This would be to complement a package of services we already provide to one of the country’s biggest players in consumer data. We use Asterisk for our IVR products already, hence why I’m here.

If anyone would like to know more about this, and there is definite possibility of paying someone a consultancy fee with the right knowledge, please PM me, and I will reveal who I work for to you privately.

I’m not exactly sure what techniques these validators use, but I’d pretty much guarantee that they have a direct SS7 connection to a telco. Just off the top of my head, some of the tricks they might use:

Do an LNP lookup and see if the database returns anything. If it does, then the number is probably active and viable. If not, try a different method.
Setup and tear down a call fast enough so the far end doesn’t actually ring. The timing requirements on that would be pretty tight, so this may or may not work. Have your SS7 gear send an ISUP IAM and as soon as you get an ACM from the other end, tear down the call.
Setup the call as an ISDN data call (this may not require a full SS7 connection). If the number is a valid voice line, the far end switch will reject the call because it is wanting a voice call, not a data call. If the number is unassigned, the far switch should return an ISDN “unassigned” call clearing code. And, of course, if you happen to dial into an ISPs ISDN dial-up bank, the call will go through, but then you can say “Hey, that’s not a valid voice line because an ISDN codec answered”. But this may trigger the far end to ring before the far end switch decides to send back an error code.

That was the sort of sneaky use of ISDN protocols that I was thinking of.

However, network operators may well consider this a violation of fair use, as it is generating a lot of signaling traffic for no revenue, and is giving information that they would either consider private, or something that they could sell, themselves.

(On the other hand, as common carriers make a lot of their money from cold calls/direct mail, they might turn a blind eye if they thought it would lead to chargeable calls to all the “valid” numbers.)

Also, note that in the UK, and probably many other countries, you must then remove all numbers belonging to people registered not to receive cold calls. (Note that, in the UK, whilst surveys are excluded from this, most ordinary people would expect otherwise.)

Thanks to you both for the info. Some useful points for follow up research.

The likely use of this type of service will be more in line with validating numbers submitted by users and pruning/verifying large customer databases. There are people already using the mobile number validation equivalent service for this purpose.

I can say for 100% certain, none of our clients will use this service for buying lists to cold call. Without exception, our clients campaigns are conducted against user lists who have opted in via a call to action or subscription.

Once again, if anyone knows concretely how to do this legally in the UK, or if you know someone else who knows, it would be great to hear from you, and I am not expecting any information for free.