If you do ever end up with an inflated bill that has come about because of illegal use of your VoIP system, and if your phone company has somehow lost the letter you sent specifying your maximum authorized expenditure, they might try and bully you into paying the bill anyway.

Phone companies have large accounts departments that are very experienced at manipulating and bullying customers to pay a bill whether it is correct or not. A recent report by analysts Juniper Research suggested that phone companies lose over $58 billion per year due to their own technical faults in billing technology. The magnitude of this figure emphasises one particular point: phone companies may sometimes underbill you, they may sometimes overbill you, but if customers were watching their bills more closely, phone companies wouldn't be making so many mistakes.

With such unreliable systems, the phone company has very little evidence they can rely on to force you to pay a bill. So they simply cut off customer's numbers.

This is why this point is so vital: use two different phone companies.

All your outgoing calls go through one company (company A).

All your phone numbers and incoming calls come through a different company (company B).

If your VoIP system is hacked or misused in some way, company A might cut off your line - but you will still be receiving incoming calls normally thanks to company B.