USB modems exist and work on Linux[0]. The Steam Deck is a Linux computer with a USB port. You could be living this reality today.

[0] https://www.thinkpenguin.com/gnu-linux/usb-4g-lte-advanced-m...

They work fine for data and SMS, but it gets complicated once you need audio routing (it's rare for a modem to expose audio over USB) or waking up from low power mode to answer the incoming call. Could be done with M.2 USB modules and some dedicated controller in-between though.

HID USB devices can already wake up computer from sleep, so i dont think we need M2 here.

Also i dont think routing audio is problem, the dongle could represent itself as external audio device, like those external usb dac.

Of course it could! Now find one that does.

Vita had a WWAN variant. What that means is, hardware wise it's trivial, business wise it's impossible. It's always has been that way. It took Apple under peak Jobs leadership couple years to sell the iPhone globally.

something like this https://en.wikipedia.org/wiki/Xperia_Play