asterisk users - Dec 2013 - How to recognize the Telco provider on outgoing calls only by sounds?

Dear list:

When I call an specific number on the PSTN, the provider who holds the
destination number give back an specified sound just after admitting their
incoming calls. Is there a way to allow Asterisk to compare sounds received
to decide what is the Telco answering the call?

I'm planning to do it to select the right provider to route further calls
at least cost.

In my country there are no public or accessible information on ported out
numbers, so it is a way to discriminate what are the destination's Telco
and build a database.

Thanks in advance!

Elder D. Arohuanca
Lima - Peru
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