How do I prevent my company from becoming a victim of these criminals?

In general, sound security practices that are enforced at every level of your company will go a long way in protecting your business from fraud. Develop a formal action plan as a “toll fraud counter measures” policy in your company. Have procedures in place so employees know who to contact (within your company and your carrier) for emergencies and what short-term actions should be taken. Work out what facilities can be cut in emergencies until security is restored.