In the IBM history series by Pugh et al, they said IBM converted punched cards to paper tape for transmission in the 1940s. My guess is that that particular transmission used telegraph TTY lines (not voice) of either AT&T or Western Union. Recall that AT&T maintained telegraph long distance lines as part of carrier long distance circuits. Because of the low bandwidth, a telegraph channel could be carried on the low end of a carrier channel. Accordingly, no modulation was required and thus no modem needed.
It was also said IBM limited development in this area to avoid annoying AT&T who was IBM's best customer.
However, in the 1950s, IBM developed card-to-card directly without paper tape and "over AT&T lines". Modems were developed to take good advtg of the available bandwidth (about 1200 baud). Undoubtedly the equipment and implementation was developed in close cooperation with AT&T.
I was wondering if the modems in that application were supplied by IBM (who appears to have developed the technology) or by AT&T. My understanding that AT&T's "Dataset" modem-telephones didn't come out until the 1960s.
Comments by anyone familiar with pre-1960 data communications would be greatly appreciated.