This is quite the tangent, but you could use regular analog modems with AMPS analog cell phones. They actually did circuit-switched analog like a wire replaceme

This is quite the tangent, but you could use regular analog modems with AMPS analog cell phones. They actually did circuit-switched analog like a wire replacement. And I used my first 2G phone as a modem to dial up my work modem bank. I believe this was on Pac Bell Wireless, before Cingular. In this GSM scenario, the phone itself had a serial port accepted modem control commands. My computer still saw it like a normal modem call, but as far as I know the digital stream was sent over the air and something on the telco side terminated it with an analog modem that called my work number over POTS lines. These were slow, somewhere in the 2400-9600 bps range. It was a capability designed into the networks, since dial-up was so important back then. You generally just had to have the right adapter cable that split out the serial (or USB) from your phone's proprietary multi-pin port.