All the data is digital (in case of BBS, mostly text, although file transfers are also possible). The analogue phone line is only used for transmitting digital

All the data is digital (in case of BBS, mostly text, although file transfers are also possible). The analogue phone line is only used for transmitting digital data over the analogue medium. The dial-up modem converts the digital data to an analogue voice signal at the transmitting end and back from analogue to digital at the receiving end. (That's what a modem is: a modulator-demodulator.) So no, you don't interact with a BBS by speech.