AT&T had wireless microwave towers for phones and tv, so I imagine there was a period near the end if its life where some dial-up connections weren't physically connected:
Working for a Midwest dialup isp in the early 2000s, we definitely served some of our smaller POPs with PTP wireless backbones, thanks in part to vast expanses of flat land with fairly tall structures dotted throughout.
https://99percentinvisible.org/article/vintage-skynet-atts-a...