Oops, sorry, I misread the post you were quoting. The thing I linked to is for phones who DO have radio and processor together and sharing memory, so the opposite of what you were actually asking.

The list includes, but is not limited to, everything that uses Snapdragon SoCs for example. Some are listed here: https://en.wikipedia.org/wiki/Snapdragon_(system_on_chip)

On the contrary, the line is quite correct in most cases. The modem processor and the application processor are in the same chip and both have access to the same memory. Further, the modem actually boots up first and it loads the application processor's kernel in RAM before starting it. (the MSM7200 for example (the HTC Hero SoC): High level diagram and Boot documentation)

So, if your modem processor is compromised it really is game over.

I think this applies much more to you than the poster. If you bothered to read the article, you would have seen that it links to a presentation about reverse engineering basebands, which clearly shows that there is an RTOS running there (REX OS)

Well, I think the tendency is that "the way modern smartphones are designed in general" is to use this kind of setup. For example, take a look at the Snapdragon SoC usage in smartphones. All of these have this type of design.

I don't know what you mean by "arbitrary hardrware" but in the android world it is normal for the modem and application processor to be in the same chip and to use the same RAM.

Take the MSM7200 for example (the HTC Hero SoC): High level diagram, Boot documentation, Software Interface Manual.

As you can see both the application processor and the modem processor are on the same chip and access the same memory. The modem processor starts up first and is reposnible for eventually starting up the application processor after putting its kernel in RAM. And there is nothing particularly strange about this configuration.