Caller is “Unknown” When Calling from Skype for Business to Some Numbers

One of my clients had a problem with some of the phone numbers they called. The recipient of the call would see the caller was “Unknown”. After some troubleshooting, I found that the number was “Unknown” to some mobile phone providers, but was good for others. Basically, all phones for some specific mobile providers would show caller as “Unknown”.

We contacted the PRI provider and after long troubleshooting, they told us that that the mobile provider told them the following: “The calling party is sending unknown numbering plan, and should update their PBX with standard numbering plan.”

This client uses AudioCodes gateway. When I checked, they already had a rule for the “Source Number IP->Tel”. They stripped +1 from the Source Number. I modified this rule and configured the following:

NPI: E.164 Public
TON: National
Presentation: Allowed

After this, the problem was fixed.


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