How? Even in the same city, cellular and land lines aren't always serviced by the same company. In most places I'm pretty sure it's illegal for phone companies

How? Even in the same city, cellular and land lines aren't always serviced by the same company. In most places I'm pretty sure it's illegal for phone companies to be swapping call data. Or are you suggesting I call back all the numbers that call me to compare bills with the owner on the other end? This plan is not going to work out.