Is that really where the goalpost is though? I thought everyone accepted that the modem itself would always be proprietary, and that was OK as long as it had a killswitch and no ability to directly interfere with the main processor or RAM. (The mostly-userland stack to drive the modem to send SMS etc. would be open.)
It seems right to me that the FCC et al shouldn't allow uncertified amateur radio firmwares.
"Is that really where the goalpost is though? I thought everyone accepted that the modem itself would always be proprietary, and that was OK as long as it had a killswitch and no ability to directly interfere with the main processor or RAM."
Most of the time when we speak about the baseband, we are talking about the telco network interface between your handset and the carrier ... and so it's tempting to think of the baseband as just some black-box modem that you can firewall yourself from.
However, the baseband processor also performs a number of real-time voice quality / noise cancelling / audio functions that really have nothing to do with the network interface, but are very important depending on how sensitive you are to call quality and things like echo, etc.
This is unfortunate because, like you, I would like to just wall of the baseband and use it as a modem and forget about it, but that perceptible difference in call-quality between "actual carrier" calls and VOIP calls is due to the baseband.
I believe that is all still true in the 2019 LTE era ...
Depends on the human defining where the goalpost is, what their threat model is and their philosophy etc. There are certainly folks who want open basebands enough to work on them, for example there are folks working on porting the Osmocom baseband codebase to Mediatek based phones.
https://osmocom.org/projects/quectel-modems/