> However, there are special circumstances in which the IRS will call or come to a home or business, such as when a taxpayer has an overdue tax bill, to secure a delinquent tax return or a delinquent employment tax payment, or to tour a business as part of an audit or during criminal investigations.

So the IRS might call if you owe taxes.

Surely moving from unsecured to a secured phone system can't be that big of a deal. In the US at least, we have experience something similar when we went from analog to digital television.

Add a secured mode of telephone calls and then telephone owners choose if they want to receive calls or messages from unauthenticated callers.