[sterlind]

Converting to text loses data and will fail on unexpected languages or accents. It's better to use a specialized voice codec, which can have fantastically high compression rates, or just keep the (already annoyingly-companded) 8kbit voice stream around in its entirety. It's pretty small.

[nezgar]

You must mean 8Khz - which results in a 64kbps stream. (8000 bytes per second) The companding was actually a very good use of 8 bits per sample for voice, introducing little artifacts except at high amplitudes and the low pass filter. Nowadays I find it ridiculous mobile networks feel it's still necessary to compress the audio further - 64Kbps is nothing on modern mobile networks, ie VoLTE etc... WB-AMR is definitely an improvement with it's 16Khz sample rate and a bitrate lower than that of G.711, but mostly not supported between different mobile carriers...

[pessimizer]

You convert it to text in order to index it. If it becomes interesting in the future, you listen to the audio (maybe after getting permission from a judge in a secret court.).