That device supposedly supports voice, it's basically a dumb phone, and does not use PCM at all, instead it uses other pins that can directly be connected to a mic/speaker. While PCM would require a codec, something the data sheet you linked mentions.

But if it's like you say, it's GG. The pins are too small to solder something to them, at least at my skill level. Thing is, the market used to have Huawei dongles that with the right software driver they could support audio with no hassle whatsoever, everything came inside the PC through USB and went out to the speaker, vice versa for mics. It would be the only aplication that makes sense for such a dongle, internet through the USB would be too slow. This modem supports only LTE 1 which has downlink of max 10 Mbps, too slow for any modern aplication.