The process of waiting to create the first packet to send (even with no compression) will always be slower than a system where you just send the audio instantly as an analog signal. Even the process of waiting for a single "sample" of audio (for a tiny tiny packet) is technically slower (but of course no one does that: they tend to group together at least 2ms of audio into a packet). The only way you can go faster than a classic land line (assuming there were no signal repeaters: like, this is one of those landlines where as you get further away the signal also gets quieter) is if you can go a shorter distance or use materials with less resistance--maybe "lower relative permittivity"? I don't know exactly what measurement you use here as I don't remember enough physics--to build the wiring or (probably your best bet) switches.