Bob wrote:

Now have 3 phones (extensions) hooked up to Verizon now.
The phones are all wired together, in parallel, in the basement.

If we go with Comcast, do we have to have new Comcast wiring to each
phone jack, or would they just pick up the connection where the 3 phones
are presently wired in the basement, without any new wiring.

Most modern housing has a demarc box outside the house. Bringing the line into
the basement and splitting it there was common on the east coast and on the east
coast. Either way, Comcast will run a line to where your room lines come
together. You don't need new wiring to each room.