For circuit-switched voice, 3G/4G dongles have undocumented commands to enable an audio-only virtual serial port that sends/receives raw audio data to the host (and you control the call via good old AT commands).
For VoWiFi/VoLTE it's just SIP with custom auth (involving the SIM card, so you need to be able to talk to it - most modems provide a way to send/receive raw APDUs to the card) on a dedicated APN so you just need to implement support for this custom auth in any SIP client (Linphone?).
Totally feasible. Or, hey, put it on an SBC, use it as an incoming SMS proxy with a dedicated SIM so you can recieve 2FA SMS without need of having the SIM and a phone with you.
You must have a SIM in the laptop at home (that's a "2FA mule") but you can use the WiFi on the phone. That helps also in other scenarios.
The last time I was in Australia I had a dual SIM phone. I put an Australian SIM in the second slot and used it for calls within the country and for data. SMS from my country didn't reach me or cost an absurd amount, can't remember. The point is that I was out of reach of 2FA SMSes and I couldn't use one of my credit cards online. Of course their customer service told me that I could switch my account to my Australian number but that never worked, it's probably a common move in scams and identity thefts. A 2FA mule would have saved me somewhat, as in some remote areas there was only voice, if lucky, and data was so slow to be useless and WiFi doesn't exist in the middle of nowhere.
Anyway, would have I left my primary SIM at home and be unreachable on my way to and from the airport? Probably not.
2FA on SMS should die. Unfortunately it's very convenient for companies. There is little setup and they can send an SMS to any random customer with little friction on customer side. No app to install, nothing.
Nothing really. I think you have to do something to make sure USB audio is routed right (I think its in their wiki). Other than that, it would work just fine!
