The issue with this is that the entire architecture trades energy consumption on the eNodeB side for the handset side. One could make a cell phone where one handset was the eNB and one the handset (and, contrary to the parent post’s claim, there would be no issue getting this approved in an ISM band), but the one operating in eNB mode would have atrocious battery life.

It also helps a lot to have one side of the transmission up on a tower with a giant high gain antenna :)