although they do exist, it's not many. it's actually relatively few.
also, if there's enough metal to interfere with mobile signals penetrating into the building, then terrestrial radio won't work either, which has a much longer wavelength and more easily blocked.
if wifi calling works, then so will streaming audio (and video for that matter).
the businesses could also get femto cells for inside the building to improve cellular, which is common for many steel and concrete buildings.