The counterargument to an all-software solution is that if you switch the profile on the Fi phone, it also remains switched if you move the SIM to another device. So however selection was made, it is 'sticky' across devices.
That's why I guessed it was a paired SIM app + intelligent Android app - but I couldn't verify that, so you could be correct.
That's why I guessed it was a paired SIM app + intelligent Android app - but I couldn't verify that, so you could be correct.