If it was impossible for the mobile calls to be made from the hijacked planes, then it follows that they must have been faked, presumably in order to get the story about invented arab hijackers across. This would involve collecting information about the passengers, creating a script, then providing operatives to impersonate everyone who made a call.
The idea that the calls is based on the claim that mobiles don’t work at altitude (see here). There’s anecdotal evidence that they do, though, and other stories that suggest otherwise. Here’s an account from a passenger of Delta Flight 1989, for instance, which was suspected of being hijacked for a while on 9/11:
...we were forced to make an emergency landing in Cleveland because there were reports that a bomb or hijacking was taking place on our plane. The pilot had radioed that there was suspicious activity in the cabin since one of the passengers was speaking urgently on his cellphone and ignored repeated flight attendant requests to stop using his cell phone while in flight. Also, there was an irregularity in the passenger manifest because there were two people [with the same middle eastern name] who were listed but only one aboard.
If true, then this suggests the passenger was able to make or receive lengthy and/or repeated calls at cruising altitude. So why not the 9/11 planes? And let’s not forget that also had Airfones, which are designed to work at altitude.
It’s far from proven that mobiles cannot have worked, then, and the idea of creating some massive operation to fake the calls seems a little bizarre. How on earth are you going to guarantee that you'll fool the family members in every case, for 50 or 100 calls? Especially when only a small number carried useful hijacking information? Remember, it only takes one family member to voice suspicions, and your whole plan could be blown open.
One supposed answer to this is that the conspirators used “voice morphing technology” to make themselves sound like the passengers:
These voices were the result of the technological wonder called voice morphing in which the sound of anybody's voice can be duplicated in real time. If the full range of the subject's voice has been recorded, which usually can happen in a 10 minute phone conversation, and then fed into the computer software, anybody speaking the subject's language can very convincingly sound like the subject person on the phone to his or her family, friends, coworkers, etc. etc.. In practical terms, problems with voice morphing will arise when gaps in the impersonator's knowledge become apparent to his or her interlocutor.
The claim appears to be based around this 1999 story:
"Gentlemen! We have called you together to inform you that we are going to overthrow the United States government." So begins a statement being delivered by Gen. Carl W. Steiner, former Commander-in-chief, U.S. Special Operations Command.
At least the voice sounds amazingly like him.
But it is not Steiner. It is the result of voice "morphing" technology developed at the Los Alamos National Laboratory in New Mexico.
By taking just a 10-minute digital recording of Steiner's voice, scientist George Papcun is able, in near real time, to clone speech patterns and develop an accurate facsimile. Steiner was so impressed, he asked for a copy of the tape.
If correct, then note that the story says the technology requires a “10-minute digital recording”. It doesn’t say that a phone conversation is enough.
Also, we’re told that the system works in “near real time”, in other words there’s a time lapse between the person speaking, and the system morphing their voice into someone else. How long? It doesn’t say, unfortunately, but it’s unsafe to assume that this system is capable of carrying out real-time conversations.
But these aren’t the only arguments against this idea. Some of the passengers weren't supposed to be travelling on the planes they eventually took:
"Jeremy Glick was supposed to have been on Flight 93 a day earlier, but missed the Monday flight after getting stuck in traffic on his way to Newark Airport... Another passenger, Lauren Grandcolas was on her way home to Marin County... Originally scheduled on a later flight, she had been pleasantly surprised to easily get a standby seat on Flight 93 at the airport. “I can’t wait to see you,” she told her husband Jack in a message she left on the couple’s answering machine before dawn in California, telling him she would be home a few hours early".
And they’re not the only ones. In fact, so many people changed their plans within around 24 hours to take this flight, that has been marked up as an anomaly in itself. A Team8Plus page (http://www.team8plus.org/content.php?article.8) points out this also applies to Jeremy Glick (missed his flight the day before), Mark Bingham (took an extra day to recover from a birthday celebration), Honor Elizabeth Wainio (changed to a direct flight at the last minute) and possibly Edward Felt (last-minute business trip) amongst those who made phone calls, and others who didn’t.
Now that does seem like a lot of last-minute changes, although without having any typical figures for comparison it’s hard to say for sure. But with regards to faking the calls, this situation surely poses a problem: how are the conspirators going to research everyone who made a call, and grab a “ten minute digital recording”, with 2 or 3 to 24 hours notice?
And as an example of the research required (although in this case not just in a few hours), consider the call by Linda Grolund, who reportedly called her sister to pass on the combination of the safe containing her will (which suggests no-one else knew it, because otherwise why bother?):
Linda Gronlund, called her sister, Elsa Strong.
Elsa Strong says, "She said, 'Hi, Else, this is Lin. I just wanted to tell you how much I love you.' And she said, 'Please tell Mom and Dad how much I love them.' And then she got real calm and said, 'Now my will is in my safe and my safe is in my closet. and this is the combination.' And she just told me the combination of her safe.