system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does phone voice quality still suck, while Skype and FaceTime sounds like the person is right next to me?
gpt
Telephone systems were deployed many decades ago and it was important that different systems were able to communicate with each other. Regulators defined standards for how these systems communicate with each other with a particular focus in ensuring that call quality was minimally clear while allowing as many conversations at the same time as they could manage. Over the years, voice communication technology has changed radically, but these interoperability regulations have proven to be politically difficult to change as few can agree on what they should be replaced with and what the costs in money and reliability might be.

Since Skype, FaceTime, and countless others are internet software applications, so internal communications on their networks don't have to adhere to telephone standards and can use modern audio encoding techniques to create much better sound quality. Some mobile phones are capable of Wideband audio, a.k.a. HD voice, where compatible devices talking over a compatible network can increase the quality of a telephone conversation.