Oswald in the doorway: the blog of the Oswald Innocence Campaign, by Ralph Cinque

This is the testimony of David Powers who was sitting right behind Emory Roberts. Powers says nothing about Robert's phone call. He says nothing about any Secret Service agent except for Clint Hill running to and boarding the limo.

"We then turned off of Main Street onto Houston and made the sharp swing to the left up Elm Street.
At that time we were traveling very slowly, no more than 12 miles an hour. In accordance with my custom, I was very much concerned about our timing and at just about that point I looked at my watch and noted that it was almost exactly 12:30 p.m., Which was the time we were due at the Trade Mart. I commented to Ken O'Donnell that it was 12:30 and we would only be about five minutes late when we arrived at the Trade Mart. Shortly thereafter the first shot went off and it sounded to me as if it were a firecracker. I noticed then that the President moved quite far to his left after the shot from the extreme right hand side where he had been sitting. There was a second shot and Governor Connally disappeared from sight and then there was a third shot which took off the top of the President's head and had the sickening sound of a grapefruit splattering against the side of a wall. The total time between the first and third shots was about 5 or 6 seconds. My first impression was that the shots came from the right and overhead, but I also had a fleeting impression that the noise appeared to come from the front in the area of the triple overpass. This may have resulted from my feeling, when I looked forward toward the overpass, that we might have ridden into an ambush.
At about the time of the third shot, the President's car accelerated sharply, with the follow-up car driving right behind it. Mrs. Kennedy climbed onto the back of the car. Perhaps she may have been looking for help and perhaps she really didn't know what she was doing. I think Special Agent Clinton Hill saved her life by climbing up on the back of the car and pushing her into the back seat because she probably would have fallen off the rear end of the car and would have been fight in the path of the other cars proceeding in the motorcade.
We proceeded at a high rate of speed to Parkland Hospital."

Why wouldn't he mention the fact that Emory Roberts was on the phone? You can't tell me he was unaware of it. If you were in a car with someone in front of you talking on the phone, could you be unaware of it?