Both concepts are correct in their own way. It depends on how the LEC chooses to handle it.
An ordinary POTS (Plain Old Telephone Service) line is an analog line from your house to the CO. Once at the CO the analog line can connect into a piece of equipment probably a channel bank or soemthing like it, which will multiplex 24/30 analog lines into a single digital T1/E1 line which then connects into the CO switch or be multiplexed higher into the digital hierarchy on its way to a switch.
In older COs (really older) it could possibly connect directly into a switch as an analog line. But that is much older technology and is rare at best anymore.
So with regard to the basic phone service to your house....it is analog. Once it gets to the CO, it more than likely converted into a digital format (PCM / Pulse Code Modulation) and multiplexed with others into a T1 and then into a switch.
I looked for link, but also couldn't find anything that may help. Hope this does.