This is just a new variant of an old attack. I have been working for a VOIP provider 10 years ago and the attack was similar: the attackers compromise a VOIP PB

This is just a new variant of an old attack. I have been working for a VOIP provider 10 years ago and the attack was similar: the attackers compromise a VOIP PBX (default passwords, extensions opened in the WAN, etc.) and then use it to call a very expensive value added service that they owned (like one special number in Tristan De Cuna or Nauru that costs 50€ at the reply and 10€ at minutes).