Emile came to America from Germany in 1870. He did not go to work directly for Bell telephone. He actualy shoveled manure at a livery in washington D.C. While hosing off his shovel he often thought about the new technology of the wireless. He was a tinkerer. He got a part time job as lab assistant to one Dr. Fahlberg (the dude who discovered saccharine) .
He studied Alexander Graham Bell’s telephone. Bells phone consisted of two identical cases containing an electro-magnet and a diaphragm connected by an electrical circuit. Unfortunately , the message transmitted wasn’t very clear. The invention had a good receiver but a poor transmitter.
Emile thought he could do better. Working alone in his rooming house he fashioned a new type of microphone which he called a "loose-contact" transmitter. It was a type of microphone, which increased the volume of the transmitted voice. It was a type of carbon microphone that varied the contact pressure between two terminals as a sound pressed against the microphone. This was much better than the crude microphones before it. Great detailed history here: http://www.du.edu/~jcalvert/tech/microph.htm
He sold out to Bell immediately and hung up his shovel. Berliner worked for Bell Telephone in New York and then Boston from 1877 and became an American citizen 4 years later. He left in 1883 and returned to Washington and established himself as a private researcher.