Happy Birthday to the T1, it's 50 years old !
A Helpful document (& MP3 audio version) that will help to understand the technology differences.
T1 and Plain Old Telephone service are in the same copper wire boxes. On the left is a very messy Aerial box. On the right is a ground box. This is nice and clean. As clean as it gets. T1 lines travel from the CO (Central Office) through a series of these boxes. Can you see how easy it is for your wires to get wet in the rain or mistaken for another wires? When Grandma & Grandpa can't hear, these boxes get opened (or remain open).