Ed Felt's phone call from flight 93 always stood out as strange.
According to the official story:
1) he made it from the bathroom of the flight using his cell phone-- so unlikely that he would have had signal/make a connection with the ground
2) he made the call towards the end of that flight, when the passenger revolt was well underway, but made no mention of that event
3) early reports had Felt describing an explosion, seeing smoke and the 911 operators hearing a whooshing sound, but that is gone from the final official transcript
4) there was serious discrepancy between the accounts of the phone call from the two people at the 911 call center who listened to it live (supposedly)
5) not clear why he called 911 rather than his wife or other family member, like most passengers did
Overall, it's clear that the phone call doesn't fit the official narrative and there has been some degree of cover-up about it.
Explanations for all this:
1) official story-friendly: Felt was scared from the beginning of the hijack, hid out in the bathroom and didn't know what was happening with the other passengers, made a 911 phone call when he thought something bad was happening with the plane at 9:58, got a lucky connection, one of the 911 call operators over-dramatized what he heard on the call, made up the explosion and smoke part, the official transcript was edited merely for clarity, parts were garbled and not interpretable.
2) conspiracy versions:
A: Felt was on the real hijacked flight 93 that was shot down, crashed in Shanksville and this was covered up
B: Felt was an actor as part of a hijack drill where a flight 93 was hijacked and shot down, he was later killed
By itself, one could possibly buy the official story-friendly version. But given all the other flight 93 weirdness: weird phone calls (e.g. Todd Beamer), the weird crash site, weirdness with the cockpit voice recorder, the known occurrence of hijack drills on 9/11/2001, I have to lean more towards the conspiracy explanations.
The official version of the cockpit voice recorder.