As you know we have multiple call servers, including an "old" one that is used by a few customers that still use NAT or IAX.
There is a setting to control this which staff can adjust. It defines which call server you are using for a specific number.
Up until now this has not been checked for outgoing calls. However, the "old" call server cannot do the same level of checking as the new call server (e.g. IP address lockdown), and it looks like this has left a possible loophole allowing calls made using the "old" call server for numbers that are configured for the new server.
We have updated the system to disallow this. If you are set to use the new calls servers (as all new numbers are) then you will not be able to make use of the "old" call server.
Staff are monitoring the logs to see if this happens so they can contact customers. However, if you have problems making calls today please contact support.