You can buy a desk phone and connect a voip line if you really wanted. Otherwise I recommend against it because you’ll learn quickly enough how bad the robocallers/spammers situation is
I wish the author had expounded on their setup. I too pay ~$1/mo for VOIP DIDs, but from what I've seen of consumer-facing prices I realize that's a facet of getting nitty and gritty with SIP (which doesn't necessarily mean self-hosting, eg voip.ms).