This was called circuit-switched data (CSD). The handset would emulate a serial modem to the attached computer and the mobile network would know how to emit th

This was called circuit-switched data (CSD). The handset would emulate a serial modem to the attached computer and the mobile network would know how to emit the correct "noises" to the far end of the connection. It was brilliant for getting into systems I managed via a dial-in modem before Internet access was broadly available. In its twilight years, carriers that had a tariff to support it would charge something like $1.35/minute to discourage its use until the tariff could be updated.