Few people remember but while most people are familiar with Walter Cronkite's voice being on CBS due to CBS being live with As The World Turns when the news broke (In fact, the first shot as ATWT hit the air. By the time the first commercial was over, news tickers AROUND THE WORLD (Except maybe China) were GOING NUTS), it was NBC's Robert MacNeil who was filing the first network radio reports (I think Dan Rather (Who ironically later went on to anchor CBS' coverage of another national crisis in 9/11) filed one or two reports of his own on network radio as well)
But shortly after the cameras came on, ONLY Robert MacNeil was on the telephone with LIVE reports (With Frank McGee relaying of course while the technicdians were working out the bugs to get Robert on the air without the need for assistance)
But again, few people remember it because MILLIONS of households were tuned to CBS at the time as CBS was THE ONLY network that was LIVE in the Eastern & Central Time zones. ABC was programming out West but it was programming a rerun of Father Knows Best & didn't have NEARLY the penetration NBC & CBS had
Not sure if NBC was feeding anything anywhere in the country or not as there's no archive (Maybe they weren't feeding anything tgo any of the time zones??)