Re: He should be proud that of that guy
Takes more time, but it means they're calling a trusted number.
And that, right there, is why you need to make sure that the corporate VoIP admin console has a good access control. There is no end to social engineering you can get away with if you have access to that.
That said, the scammers that set up their VoIP system to represent a national number appear not to have worked out that an inland call will not show the international prefix (i.e. a UK originated call to a UK number will not start with "0044") so such a called ID makes it easy to reject the call :).