So many things wrong with this:

  1. That’s a fax machine handshake not a data modem.
  2. That’s a LOT of data to be hissing over dial-up in a highly compressed GSM voice channel. That kind of interface would be pushing it even on 10 Mbps broadband.
  3. The background noise would have had that handshake repeating over and over

Credit to @riskable@programming.dev for their comment in another thread that inspired the post title.