Its not possible to filter all calls that originate on VoIP. Once a call is on the PSTN, they're all the same.

The only way would be to set rules such as flags or certain number ranges, but you'd be relying on the sender to be honest. You may as well ask them to set a spam flag.

And VOIP is becoming more and more popular, even for residential lines. All new lines over here seem to be VOIP by default these days. You have to specifically ask for an ISDN line if you don't want VOIP.

And then people are using things like Skype Out for calling numbers in other countries, as it is cheaper than using the normal land line.

why not just Skype call them? After all, that's free. Aside from the point that while Skype calls have grown, the volume of skype-to-phone calls is still a minute fraction of the number of phone-to-phone calls. So you're asking for convenience for a small minority at a cost of inconvenience for the large majority. That's not generally how things work.

Because they don't have computers or Skype and I get a free hour of Skype Out every month and even if I call from my house 'phone, that is also VOIP.

Most providers use VOIP to make calls, it's the most cost efficient way of doing things

It would make sense if there were some way to block any call if it could not be verified either way. That would allow VoIP to continue.

There are (or were - I assume you can still get them) boxes which sit between your phone and the socket. If the number is on a white list, the call gets through. It not, it is blocked and the caller is given an opportunity to record a message. If the recipient wants to receive the call, they can pick up the phone. If not, the call will be declined.

I saw this a few years ago, and given the volume of junk calls we were getting, I was really considering getting one of these boxes. If the call is a proper dud, you don’t even get the phone ringing.

Earlier this year, I was screening calls because of the junk we were getting. My policy now is that I won’t rush to the phone when it rungs. If the call is important enough, they’ll leave a message. If not, I’ll try 1471 and see what the number was.

That is all well and good though it does mean spending money to resolve a problem not of your making. I do use caller ID which again should be free so that I can avoid calls, especially if there is no number displayed.