Phone system hackers of my distant acquaintance, two of whom have done federal time for messing with phone systems have made this statement. This is not "CALLER ID" that shows up in your handset, that can be easily faked.
The call data is the data used to generate your phone bills and the phone company takes very good care of it.
Yes, it could be faked just like the books for the bank can be faked if you have enough people inside the company and in on the scam, but it's lots of people for the phone system or the bank.
In any case, the Felt's call data is consistent with everything else we know about Flight 93. You'd have to fake lots more than the call data to keep a consistent story.
IMO, 70,0001 people would be about right for the number of people involved with faking the standard story of the hijacking of the 4 planes.
I've been on the white-hat side of hacking, some of it in a professional capacity since about 1980.
1. Gravy's estimate of the number of people involved with the recovery and investigation of what happened on 9/11.