[Considered1]

On call works from a hidden sim in the car.
You will only need a sim if you also want to set up wifi in the car, but you can always tether your phone.

Not sure if it's been upgraded in the new XC90 as mine is just a standard sim and it's only 3G (even if you put a 4g sim in there).

Hopefully someone might be able to confirm it has moved with the times.