This is one of the differences between the PinePhone and Librem 5. They both have hardware switches for the modem, however the modem can be removed entirely from the Librem 5. I wonder what the hardware switch in the PinePhone is disabling. Is it power? The modem module on Librem 5 adds about 5mm in depth compared to the PinePhone and has the switches on the outside. The switches on the PinePhone are under the back cover and fits with the use case of setting it and not touching it again — could even epoxy it.
Discussion
The switch on the pinephone is for the power to the modem. All a bit fiddly, but it works. Cost difference is big too!
The pp's disadvantages is seems a little fragile, h/W switches under rear cover, battery life maybe 2 days on standby, camera not very good.
Advantages: price & availability, easy & inexpensive to repair. Open source modem firmware. Pp pro is more expensive. Both can have cover keyboard as extra, & can work well as desktop with adaptor.
Great! Looks like schematics are available too.
https://wiki.pine64.org/index.php/PinePhone#Privacy_switch_configuration