> AAC makes a lot of sense for low- and medium-quality applications where bandwidth is extremely limited or expensive, like phone calls and music-streaming services, or as sound for video, for which it’s the most widely supported format.

Nope; you can scratch "phone calls" from that list.

AAC (specifically, the AAC-LD variant) is not the best for low bitrate calls; you want a dedicated voice codec for that application.

https://en.wikipedia.org/wiki/AAC-LD

AAC-LD is only geared toward voice in one parameter: frame size. It's basically just a "look, AAC can do this too if you want" feature.

Look at the remark there: "It can use a bit rate of 32 - 64kbit/s or higher". That's a whopping lot. 32 kbps is about the far-out upper bound on bit rate for using a voice codec. You can get very good call quality at half that.

http://opus-codec.org/comparison/

Basically if you look at all the options for compressing speech in telephony, AAC doesn't make a whole lot of sense.