Arguably these have a function; consumers got used to them from multi frequency dialing in the past, so if you're used to the tones it provides an additional so

Arguably these have a function; consumers got used to them from multi frequency dialing in the past, so if you're used to the tones it provides an additional source of error correction (for example to find that you pressed 5 twice instead of 52 which you intended). The frequencies are there for historical reasons, but they do have a purpose.