If that's what these were. And the origin would be known. At least, it would be known that it was airfone to operator. Other details of it would therefore presumably be withheld, not "unknown."
It's an interesting stipulation, don't you think?
From p. 329ff.:
MR. RASKIN: Your Honor, I would like to read from the
6 stipulation again.
7 THE COURT: Yes, sir.
(...)
At 9:12 a.m., flight attendant Renee May called her
10 parents on an air phone. Ms. May told her mother that her flight
11 had been hijacked by six men who had moved them to the rear of the
12 plane. Ms. May asked her mother to call American Airlines to make
13 sure they knew about the hijacking, giving her three Northern
14 Virginia phone calls -- phone numbers to call.
15 Between 9:12 a.m. and the time Flight 77 was crashed
16 into the Pentagon, Renee May's mother called American Airlines at
17 Reagan National Airport and conveyed the message from Ms. May that
18 Flight 77 had been hijacked.
19 At 9:15 a.m. and at 9:26 a.m., Flight 77 passenger
20 Barbara Olson called her husband, Ted Olson, and spoke to him for
21 about one minute before the call was cut off. Barbara Olson
22 reported that the flight had been hijacked by hijackers wielding
23 knives and box cutters and that all the passengers were in the
24 back of the plane.
25 At 9:20 a.m. and 9:31 a.m., Barbara Olson again called
331
1 and spoke to her husband, Ted Olson. She reported that the pilot
2 had announced that the flight had been hijacked. Ted Olson asked
3 Barbara her location, and she replied that the plane was flying
4 over houses. Ted Olson told his wife of the two previous
5 hijackings and crashes.
FBI Presentation -
Times of "unknown number" calls
1) 9:14:57 ("on button pressed," presumably 0 sec.)
2) 9:15:34 (102 sec.)
3) 9:20:15 (274 sec.)
4) 9:25:48 (159 sec.)
5) 9:30:56 (260 sec.)
In-Court reading of "Stipulation" -
Times of Olson Calls, listed in confused order
1) 9:15 a.m.
2) 9:26 a.m. (first two lumped as "about one minute")
3) 9:20 a.m.
4) 9:30 a.m.
So the four "stipulation" calls from Olson match the four connected calls from/to "unknown number" according to the FBI presentation (2-5) for start times, albeit with a lack of clarity as to duration in the stipulation.
The question remains: Since they're in the stipulation, why does the FBI consider these "unknown," giving rise to the confusion? Where did the stipulation info come from, if not the FBI?
Also weird, but can be chalked up to confusion:
She reported that the pilot
2 had announced that the flight had been hijacked.
The pilot?
Meanwhile the Renee May call in the stipulation matches the one identified by the FBI presentation as from her. She mentions six hijackers, but this can be confusion, too.
NOTE: Thanks for linking to that, by the way. And I need to finally learn how to spell Olson.