GitHub - jtarrio/SoftwareModem: An implementation of the ITU-T V.21 modem standard, working on a PC over a sound card.
DSL-Warehouse
Zoom H08-03328-C Accura V90 External Modem 56Kbps RS-232 (Serial Port) Bell 103, ITU V.17, ITU V.27ter, K56Flex, ITU V.21, Bell 212A, ITU V.22, ITU V.22bis, ITU V.29, ITU V.32, ITU V.32bis, ITU
SHDTU03-V35/2T-AC, 2-wire TDM V.35 NTU Modem with DB25M to MB34F Cable (0.2M)
U.S. Robotics Courier Lite 56k Dial Up Business Modem - Serial - 56 kbit/s - ITU V.17, ITU-T V.29, ITU-T V.27ter, ITU-T V.21, EIA 578 Class 1, EIA 592 Class 2.0, ITU-T