We’ve all heard that Mother’s Day is the busiest “calling holiday” of the year for phone companies. This article on the call volume clears up the actual numbers, based on Verizon’s data. On a regular workday, 1.5 billion calls are made at Verizon and on a regular Sunday it’s 870 million calls. Mother’s Day is expected to bring 1 billion calls at Verizon, which serves 29 states. And Mother’s Day is the second highest day for collect calls. Number one? Father’s Day.