Do cellular modems really "need" to do audio any more? I don't mean because everyone could just be using data-only SIMs with OTT SIP software. I mean, instead: sure, audio is part of the cellular
standards—but why is it part of the cellular
baseband hardware? Phones aren't made in a way where the baseband chip "is" the phone any more. The modem is now a tiny part of the processing power of even the dumbest of dumbphones.
So, given this, why can't the standards require that the modem expect there to be some other chip (e.g. the SoC in a smartphone; a specialized DSP on a dumbphone; a ground resistor on a mobile data stick) to feed the modem audio packets which have been pre-encoded and serialized to the format it would have done itself, so it can just take them, wrap them in baseband frames, and directly put them on the wire?
In other words, why is the (DAC + GSM/G.722/etc. DSP + ser/des) logic a feature of cellular modems, rather than a feature of phones?
Think about it by analogy: you wouldn't expect a PSTN modem to come with a feature where a computer can make analogue telephone calls using it by hooking it up directly to your microphone and speakers. You'd expect that, if it did any such thing, it'd be by DMAing pre-encoded-for-the-wire packets out of a realtime ring buffer, the same way any network card consumes any other packet. Maybe your sound-card would provide hardware support for some codecs (by consuming one DMA ring and producing another. Or maybe you'd do the audio encoding on your GPU with a GPGPU shader, allowing your phone to speak new voice codecs with just a firmware update.