When I was younger I had this friend (cof, cof) who used to war-dial 0800 numbers (telephones beginning with 0800 are national toll free numbers in Brazil) looking for modem tones.
The biggest share of toll free numbers with modem tones were fax machines and but many were 9600 baud terminal for some CLP. I guess these were remote maintenance accesses for isolated machinery - I wonder if people still do this (may be an updated version with 3G or 4G).
The biggest share of toll free numbers with modem tones were fax machines and but many were 9600 baud terminal for some CLP. I guess these were remote maintenance accesses for isolated machinery - I wonder if people still do this (may be an updated version with 3G or 4G).