You can't hear this mechanical voice anymore. AT&T stopped offering this service at the end of last year. According to NPR, a recording of the voice of the last "Time Lady," Joanne Daniels, will be put in the Smithsonian! I would link you the audio but I can't find it. Instead, I'll point you to this article that cheesily proclaims, "Time has run out on the Time Lady." The service started in the 1940s but was obviously already well known enough to be referenced by Raymond Chandler in 1953 in The Long Goodbye, a book I highly recommend.
And when she spoke her voice had the lucid emptiness of that mechanical voice on the telephone that tells you the time, and if you keep listening, which people don't because they have no reason to, it will keep on telling you the passing seconds for ever, without the slightest change of inflection.