What position do cellular communcation (1G, 2G, 3G, 4G or other function only implemented in phone) play in Android operating system archtecture?
If it is in kernel layer, it means that there should be an independent kernel repository or patch specific for cell phone other that tab computer, smart television and music player. It would not be a good design of architecture and will be difficult to maintain.


Bingo. Lots of device specific stuff are in binary blob drivers which only work for specific devices. Android has no common platform like a PC. Those drivers are held by the device manufacturers or system-on-a-chip vendors.

See: Why is it that Android still can't be installed as regular OS?, and Why are there not generic phone OS installers?

Based on this article from LWN.net: An update on the Android problem is seems like the Android kernel problem is improving, but architectural changes like Project Treble would only benefit devices already integrated with those changes.

And so posts like Is there a technical reason Android update story is so bad? will remain valid for some time.

If you wish to go down deeper, at least be aware of the content in the AOSP Architecture documentation

Yes, but what about cellular radio

Mobile telephony radio is managed via a baseband processor which will have its own CPU/RAM/Firmware. Control communication appears to be done by serial AT commands. Realize that baseband processors may differ based on device model.

For more detail see:
How mobile OS talks to baseband OS and How does Modem code talk to Android code

But why doesn't it boot?

Flashing software that isn't specifically designed for the hardware could/would result in bricking. A quick check of the specs for a Samsung Galaxy Note II shows two different CPUs - Exynos and Qualcomm. While both may run ARM code, the internal architecture is different: i.e. number of cores, GPU driver, camera driver, memory layout etc. Putting a US AT&amp;T firmware, designed for Exynos, on hardware for China Mobile, containing Qualcomm, is guaranteed won't work.

Response to Update 1

While the CPU chipset may be the same, GT-N7108 radio band support for the USA is poor with no 3G bands, which means that the physical baseband processor would be different for Galaxy Note II models marketed and sold in the USA. As part of the boot process, the baseband processor is checked (further details in prior links), that could easily result in a non-operational state.