The hard part is not the modem design per se.

The hard part is designing a good modem while also unambiguously working around all the Qualcomm patents in all the jurisdictions that have iPhone, which is all of them.

Because if you don’t do that, you’re still paying Qualcomm which defeats an important purpose of making your own modem.

I would buy that a decent modem is harder than many CPU designs, maybe even most. But harder than state-of-the-art? Surely not, have you seen the complexity?

And even CPUs (esp state of art) have to worry about radio effects, as in avoiding internally and across chipset.

s/work/patent blackmail/g