MEGAphone: Cellular Modem Voice Circuit Control

Okay, so I have SMS working already, and a nice library to let me send and receive them, complete with emojis and international characters etc. But what I don't yet have is the voice call control working in the same way. The reason being that the EC25 module I have, while supporting 4G, lacks VoLTE support for the Optus Network in Australia. I've poked the support at Quectel who make the modem,…