There's an awkward, intermediate step, sort of like what we had with 1G cellular: while the signalling was all digital (but not IP), the actual voice payload wa

There's an awkward, intermediate step, sort of like what we had with 1G cellular: while the signalling was all digital (but not IP), the actual voice payload was carried on a dynamically-provisioned analog channel. We had Merlins at my parents' store when I was growing up, and an interesting artifact of the analog channel was that some analog data was possible. For instance, we hung a fax off one of the Merlins (14.4k was fine); I likewise got get 33.6k off it when I plugged in my modem, but could never get 56k. In hindsight, that's because 56k actually requires the line to support digital signalling, which the Merlin did not.