https://www.fcc.gov/oet/ea/rfdevice
> INTENTIONAL RADIATORS (Part 15, Subparts C through F and H)
> An intentional radiator (defined in Section 15.3 (o)) is a device that intentionally generates and emits radio frequency energy by radiation or induction that may be operated without an individual license.
> Examples include: wireless garage door openers, wireless microphones, RF universal remote control devices, cordless telephones, wireless alarm systems, Wi-Fi transmitters, and Bluetooth radio devices.
https://www.ecfr.gov/current/title-47/chapter-I/subchapter-A...
Other countries have similar regulations.
PCs don't have that restriction.
You might be able to get to the point where you have a broadcast license and can get approved to transmit in the cellphone radio spectrum and get FCC approval for doing so with your device... but if you were to distribute it and someone else was easily able to modify it who wasn't licensed and made it into a jammer you would also be liable.
The scale that the cellphone companies work at such liability is not something that they are comfortable with. So the devices they sell are locked down as hard as they can to make it clear that if someone was to modify a device they were selling it wasn't something that they intended or made easy.
And a huge reason it seems like BS is this:
> PCs don't have that restriction.
There are obviously PCs with Wi-Fi and even cellular modems, so this can't be an excuse for a phone to not be at least as open as a PC.