This works fine for calls from your landline or cellphone. It doesn't work as well go businesses which may legitimately split incoming and outgoing service, so the outgoing carrier really has no way to know what source numbers are legitimate. There's also a pretty big business in traffic resale, and none of those guys have any idea.

What would be more useful is accessible path information, so I can complain to my carrier about a call, and they can find out where it came from and throw people or companies off the network.

"so the outgoing carrier really has no way to know what source numbers are legitimate."

It shouldn't be difficult to get a single number that is legitimate and limit the caller id to that number. Any telecom carrier whose customer is requesting a wide variety of phone numbers ought to know that something sketchy is going on.

Let's say I'm a not entirely small company, with employees with phones on their desks who call customers and have direct numbers to be called. When they call out, the caller id should be their desk number so the people they're calling know it's them and answer the phone.

But the carrier that handles inbound calling charges an arm and a leg for outbound, so I'd like to use another carrier for outbound; I don't want to change my inbound carrier.

In that case there should still be some similarity among the numbers (area code, exchange, etc), and it wouldn't be difficult to tell the outgoing provider that you're going to be using a particular block of numbers. At a minimum, the outgoing calls shouldn't have numbers from different area codes every day.