Early Speech Synthesis

Here  is an example of one of the first vocoders(VODER: Presented at the Worlds Fair) in 1939. It's incredible to listen to the sounds, and hear how each tone is used to vary the expression. It's now common to have computers talk to users via vocoders (Siri, Salli)

As an example of the progress sound synthesis has made, this  is a link to a Japanese android which sings using synthesis. The company is currently working on adding human breathe to the sound, to make the melody sound more natural. A practice of this being used daily would be Steven Hawking who uses Speech Plus (made in China) to verbally communicate and would other wise not be able to. 

The industry of speech synthesis is very competitive, this article does good job of explaining the history vocoders.