A thoroughly obsolete 1200bps Racal-Vadic thing that didn't do the Hayes command set. Its command set was sufficiently different to AT that I couldn't configure my terminal program to control it, so I'd pick up the phone, dial whichever BBS I wanted to call, wait for the beep, push the connect button on the modem's front panel, and put down the phone.

I think it was sufficiently obsolete that the BBSes I called would have had 9600bps or 14.4kbps modems by then.

Found the manual! https://usermanual.wiki/m/e841e449995c65b1eb3d261c6cec7d97d5b42039de6114e9fed37628782b868a.pdf