Don't remove POTS. Some key reasons:
In case of incident (Natural / man made). Here in Seattle (area), several years ago we had a large wind storm that took out most of the power in the entire region. Many areas didn't have power for over a week. Cell phone - towers died after about three days. That's right: The TOWERS failed. Also, you couldn't get gasoline; no power at the pumps (Read local generators - at homes - started giving out).
In some areas of Seattle, people have their choice of which ISP they like (DSL, Cable, fiber optic, wireless) which is all fine and good for a VOIP carrier. Ask any of the phone companies what will happen when the power goes out? You can't call... 911, the power company, anyone for any emergency service, much less a call such as "I'm alive and okay", or "need food, shelter" (in case of some emergency).
I have family in north eastern WA. Where they are at, there is not viable alternative to dial-up. No VOIP, and spotty cell phone availability.
Cell phones... great sound unless you are in a dead area (there are a lot more of these than the phone company's are willing to admit); or as noted the power is out for an extended time.
Just because it (POTS) isn't as profitable as cell - or as well regulated, doesn't men it should be dismantled.