alt Hacker News>But somehow pushing the modem in the MacBook solves this...because Apple is then good at managing transient network connections in macos, hooking to complex mesh networks on protocols they don't control ?
A cell modem is mostly just another uplink, with all the hard stuff being done in the modem. The user doesn't need to do anything to use it. Tethering requires extra stuff to happen: the user has to initiate the connection, the iPhone has to reconfigure its networking, and I imagine there's a bunch of security layers that must be passed through before tethering is allowed. It's 2 entirely different scenarios.
You choose to simplify how to integrate the modem into the system while digging deeper into how tethering happens.
Why doesn't having another separate subsystem running it's own OS managing the cell connection also have network switching implications (something deciding the connection is now the primary one, just like it does for tethering), security issues (it's a know attack vector on phones as well), power management issues etc ?
The iPhone 3G for instance was a piece of crap network connection wise, it would drop calls, lose signal, memory leak at the border of the two systems etc. Networking with a cell subsystem isn't trivial.