I've been told the 'voice' we hear from cellphones is actually a (good) reproduction of the voice - as opposed to the old copper wire landline system transmitting an actual voice.
The digitization process looks up what sound the words are making and it assembles the transmitted 'voice' from a file. If you've ever heard music over a cell phone, you probably remember the music doesn't sound so good. It's because of this file lookup and digital translation. The music isn't in the translation file so the fidelity is much lower. :-)