Verizon Select Services verified on-the-line with the automated system. I can't find an operator who does that. The automated system ignores anything from the caller's side. A 3-way call wouldn't work because as far as the IVR is concerned, you're one person.
An AT&T operator did verify on-the-line, but she conferenced in an automated system. The automated system didn't allow me to say anything - it ignored everything from my side.