That is debatable: the principles behind the analog side of RF haven't changed all that much in the past 30 years, what did change is the the amount of DSP power we can afford to throw at signals once they reach the ADCs. 30 years ago, we were limited to what could be done using analog detectors and decoders because digital processing wasn't economically viable in the consumer space beyond trivial signaling rates. Today, we have affordable 10+bits ADCs and DACs that can operate at over 1GSPS and DSPs that can process 200+MHz worth of spectrum per input/output channel with enough headroom to afford pushing the science and math closer to theoretical limits.
It is more about the software than the hardware at this point.
It isn't the modems that are troublesome, it is all of the patents and royalties that need to be mitigated if you don't want to get run out of the market like what Qualcomm was trying to do to Apple to get Apple to drop Intel. Uncertainty about Intel's ability to deliver was a convenient excuse for Apple to settle with Qualcomm by scrapping the Intel deal.
SoC design shops don't do modems because they are a patent, licensing and regulatory nightmare.