Here it is, a 48K VBR mp3:   h

 The call's a dub at the end of  to the recording of the participants
discussing the event, apparently immediately afterwards.
Note the statement by one of the staff that he's hearing that in one ear of
his headset, and the current  discussion through the other.  A comment's
made that the delay is about 1/4 second.

The disk from which I transferred this (to 15 ips tape) circa 1976-1977 was
a 12" diameter vertical cut 33.33 rpm colorless translucent ACETATE
PRESSING. (Please let us not again get into the discussion that AT&T did
not press in acetate). I've tweaked this version to make listening more
comfortable than it is in its raw form:  suppression of the low level /
high frequency clicks that occasionally occurred, hard limiting, and a
steep 5KHz low pass.  There's NO manual gain riding. The duration's
nominally 9:42.  One of the participants, Walter S. Gifford was at that
time AT&T's President.

I probably had not run that tape in 35 years.  It ran and played back
properly.  And why shouldn't it have? The stock's 1.5 mil. UNCOATED Maxell

Now, a call for help from our UK participants.  The recording of the first
official phone call between NYC and London (January 7, 1927) was made here
in NYC.  The two most likely venues were the AT&T Corporate H.Q. at 195
Broadway, or at Bell Labs on West Street.  It's more of a two way
proclamation by Gifford and Sir Evelyn Murray, the British Post Master
General (is that title correct) than a 'real conversation'.  BUT, there's
considerable static when Murray speaks.  IF it was also recorded in London,
then a clear recording could be assemble-edited.

If any of you have connections (pun intended) with feasible sources , then
please try to assist.

Art (Shiffy) Shifrin