Were phone calls from UA 93 recorded or not?

[John Doe II]

Were phone calls from UA 93 really not recorded?

Todd Beamer's phone call was definitely recorded according to all accounts as this is a standard procedure by Verizon.
http://www.post-gazette.com/headlines/20010919gtenatp3.asp
Tom Burnett's second, third and fourth phone should have been recorded as the FBI was listening in.
At least the last 20 minutes of Jeremy Glick's call were recorded.
http://www.timesunion.com/AspStories/story.asp?storyID=57018&category=FRONTPG&BCCode=HOME&newsdate=9/8/2002
http://www.post-gazette.com/headlines/20010913somersetnat3p3.asp

Theses are the three longest and central phone calls of the flight.
First of all let's state that the claim that they have been recorded is exactly what one would expect if the FBI was listening in during theses three calls. This was the case in all three calls according to many media accounts and Jere Longman's book "Among the Heroes".

Due to an interesting question of Astro3 I checked out the Commission Report and found something noteworthy.
While Betty Ong's phone call is always in the footnotes referred to as "transcript" (indicating that the Commission used the transcript of this recorded call) this is in none of the any call from UA 93 the case! the Commission refers in its footnotes only to interviews of recipients of the call never of an actual recording.

This of course leads to the question:
Do any recordings of theses phone calls exist?
And if not how is this explainable?

[philb]

1. There is a recording of Amy Sweeney's call; but it hasn't been made

public. Why?