Were the phone calls placed on Flight 77 and Flight 93 impossible/fake??

I've been interested in the 9/11 conspiracies for quite some time. I've watched a few documentaries, the best one being The New Pearl Harbour by Massimmo Mazzucco. I've also listened to David Icke on his London Real interview.

A part that interested in me was the idea that the phone calls were doctored through voice morphing technology or that the passengers were co-erced. The reason being apparently is that it was and still is impossible for an average phone to make a phone call above 10,000+ feet. The airliners were travelling at their crusing altitude and only one person made a phone call on Flight 77 (Barbara Olson). David Icke suggests that it's impossible but that it could also not have been a in-system flight call as the phones were decommissioned on the Boeing 757's.

On Flight 93, multiple people made phone calls to their loved ones, some from phone calls and some from in-flight phones but again, the plane was travelling way to high to make phone calls from a cellular phone.

The other thing noted was the lack of background noise the 9/11 family members of the passengers on Flight 93 reported.

The last key piece was the fact that a phone operator who was talking to Todd Beamer had her phone simply go silent after the "Let's Roll" plan to overthrow the hijackers. The operator stayed on until she learned that UA93 had crashed in Shanksville. She found it odd that it didn't made the standard beeping noise that phones make once either party unexpectedly loses connection.