Prior to this Bell telephone hadn't advertised much on radio. their ad dollars had been spend mostly on print adverts. (Hey, when you're already a monopoly you don't have to try hard.) So two decades behind the trend, Bell began sponsoring the concert series on April 29, 1940. Assistant VP John Shaw started researching the possibilities for a radio program as early as 1930. He recommended in 1931 that they bite and launch a program. The idea sat in limbo for 9 years. In 1939 the FCC took Bell to task for it's relationship with radio.
"The Bell system does comparatively little advertising by radio, despite the fact that it is one of the beneficiaries of radio broadcasting through the leasing of circuits for program transmission service."
It was no criminal indictment, but it pointed out a one-way relationship at the hands of a monopoly. they implied much more than they actually said. Bell was producing sample programs within just a few months. It was produced by the N.W. Ayer Co. with assistance from Tommy Cook at AT&T. They assembled a 57-member orchestra mostly made up from members of the New York Philharmonic and the Metropolitan Opera. During WWII an AFRS version of the program was recorded under the name "Music From America. In the late 40s a few short films were made of the rehearsals and backstage banter. It continued on NBC until June 30, 1958 when they prepared for the jump to television.
It continued on television from 1959 to 1968. Throughout the program's run on both radio and television, the studio orchestra on the program was conducted by Donald Voorhees. The TV version of the program was a bit more interesting, they even had Johnny Cash as a gust on a western-themed night. In 1978 Bell telephone magazine bragged that during its run on radio, the Bell telephone Hour was the "oldest, continuous nighttime network program in American Broadcasting." It might well have been true too... with all those caveats included.