Ideally there would be a ANI number, which should be the originating number. Which is used to know who to bill as the call goes from telco to telco. Most phones

Ideally there would be a ANI number, which should be the originating number. Which is used to know who to bill as the call goes from telco to telco. Most phones don't use this, it isn't required and can also be spoofed. Then there is the CSID which is what shows up on your caller ID and that can be set to whatever we want. What we really need is to force ANI because that is transmitted before the first ring and the CSID is after the second ring. But hardly anyone wants to have a ANI set, especially the spammers.