Yes, it was clunky and big. But if you reduce it to palm size and streamline it, this 1907 Western Electric Model 317 Phone (in production for 30 years) has an ideal user interface. There is one "button," the hand-cranked ON switch. There's no other buttons, no menu, no screen. You just talk to it (the local human operator was the OS), tell it who you want to talk to, what you want to do.
This phone interface is 100 years old. It is the phone interface of the future. Seriously. (Tip o hat to Jason Bobe)