At 4:30 P. M. here, when it was 1:30 in San Francisco, John J. Carty, chief engineer of the company, announced that all was ready, and Dr. Bell picked up the receiver in front of him as Mr. Watson, in San Francisco, picked up his receiver. Then speaking in an easy tone, Dr. Bell said:
“Mr. Watson, are you there?”
And Mr. Watson replied that he was and that he heard distinctly. Thus was the first human voice heard across the continent. The hundreds at both ends of the line broke into enthusiastic applause

☛ The New York Times: “Phone to Pacific From the Atlantic. Perfect Test of Transcontinental Line Made by Inventors of Bell and Watson”, January 26th, 1915, Front Page (PDF)

It gets better:

The telephone line used across the continent yesterday will be opened for commercial purposes on March 1. It was announced that the charge for a telephone conversation between New York and San Francisco would be $20.70 for the first three minutes, and $6.75 for each minute thereafter. When one man in New York talks to a man in San Francisco $2,000,000 worth of apparatus will be tied up and cannot be used for the duration of the conversation for any other purpose. It is expected that, in normal conditions, it will require about ten minutes to put a call “through” across the continent.
In the line there are two physical and one phantom circuits and in each physical circuit there are two wires and 6,800 miles of hard drawn copper wire. There are 870 pounds of copper wire in each circuit mile and 2,960 tons in the entire line. The line crosses thirteen States and passes through Salt Lake City, Denver, Omaha, Chicago, and Buffalo, with a branch that runs through Pittsburgh, Washington, and Philadelphia. In the main line there are 130,000 poles.

First spotted via Alexis Madrigal’s blog.