The ability of the east coast of the United States to communicate with the west coast was FIRST made possible by what?
The Pony Express
While it only lasted for a short time the Pony Express was the first means of "rapid" communication between the East and West coast.
Pony Express riders would ride running horses across the western united states carrying mail and messages. The riders would change horses and keep riding. The express bags would be handed off to another rider with no break in the speed of the horses.
This method of communication was expensive and difficult. Difficult terrain hostile Indians and bad weather made the Pony Express a questionable enterprise.
The telegraph soon replaced the intrepid riders of the Pony Express.
The romance and the legend of this first method of communication lasted much longer than the reality.