This radio transmission clearly mentions a list of demands! If indeed this transmission is coming from Flight 93, then the hijackers believe that they are planning to land the plane at some point and trade hostages for whatever those demands are. They do not appear to be aware of a plan to crash into a building. More to the point if this is what the hijackers are saying, then this is what the passengers of Flight 93 also think.
And here is the most important part. From the transmission about a list of demands to the first report of a puff of smoke in the air where Flight 93 was flying at altitude is just 45 seconds. From the transmission about the list of demands it is clear that the hijacker is untroubled by any unruly passengers. We know the plane is at 35,000 feet altitude, as that is the confirmation the controller is asking for as the tape starts. The only way that United Airlines Flight 93 could have crashed in the 45 seconds after the second transmission regarding the list of demands would have been to point nose directly down and power down the whole way without any interruption. This leaves no time for the passengers to burst through the door, or the hijacker pilot to react. Any struggle over the controls would have sent the plane spiralling across the sky, pointed up as much as down.
Therefore, if these radio transmissions are genuine, we now know two facts. The hijackers were talking about a list of demands, not suicide. And the story of the passengers crashing the plane during a fight with the hijackers simply could not have happened that way.