IBM System7use of Teletype as console 2546

IBM did make PBXs - PABXs actually - but they were never sold in the US. I believe the 2750 was the only one that was even moderately successful, but there was also a later 3750, and a smaller 1750. The processor (at least for the 2750 - not sure about the others) was an 1130-1800 machine. ROLM wasn't bought until much later.

At the time these were being sold (1970s), it was still a very regulated business, and there were very high costs buttociated with getting the machine homologated -- this means getting the approval of the operator of the public telephone network -- before it could be sold and connected. In addition, there were variations in the switching used on central office trunk lines from country to country which necessitated the development of country-specific line cards, and this further increased the cost. Many of the national PTT organizations, at least in Europe, had cozy relationships with a specific vendor, sometimes one in the same country, and these vendors had a natural advantage in also being the provider of PABXs in that country.

And the reason the System-7 used a teletype was strictly a cost issue. It was also a more "natural" choice given the target environment, but cost was the dominant consideration.

Peter Capek