[BC] putting phone calls on the air

[Donna Halper]

This is a semi-historical query.  I found an old clipping from 
January of 1929 (!) wherein a Minneapolis/St Paul announcer 
successfully put callers on the air.  I know that back then, the 
Federal Radio Commission (later the FCC) did not permit phone calls 
to air-- I thought it was because of technical problems that were not 
yet resolvable in the 1920s, but also the FRC seemed to think phone 
calls were "point to point communication" rather than mass 
communication.  Anyway, I was wondering when did radio stations begin 
putting callers on the air on a regular basis?  I know that there was 
a KDKA talk show with Ed and Wendy King in the late 40s or early 50s 
that had callers, but the hosts had to paraphrase or repeat what the 
callers said rather than put them on the air... so when did that all 
change, and what led to the change taking place-- was it in fact 
improvements in technology?