In the over-used telco jargon "POTS" stands for Plain Old Telephone Service. We also call it the Publisc Switched Telephone Network (or PSTN). AT&T has described POTS in the US as ‘relics of a by-gone era’ and has called on the Federal Communications Commission (FCC) to set a date to scrap it.
As we understand that today it consists of a twisted pair of copper cable from the customer to a telephone exchange. That exchange is these days a big computer (an SPC switch) that is also known as a "Class 5" switch - the switches used for local access. What we get as a service is a simple "analogue" telephone.
AT&T isn't saying the telephone is dead, just the means of delivering it. They (as they have remorphed into being one of the former "baby bells") are complaning about the regulatory striictures requiring them to maintain their existing POTS networks when they want to invest in something else.
It is worth remembering that it was just the same desire by Telstra that started our NBN journey. Their 2005 proposal for a Fibre to the Node (FTTN) network was accompanied by replacing all their voice switches with "five paired soft switches". They share the concern with AT&T with the need to call "time" on the PSTN - with one regulatory officer famously telling a Senate Committee that it was five minutes to midnight for the copper network.
This is all a really important message for NBN Co, the Government, Telstra and Telstra's shareholders to understand. Building a nice shiny new FTTH access network for Telstra is doing them a favour - there is no need for special "compensation" for moving their customer base.