On Sept 11th, 2001, Hijackers took control of four planes which resulted in the attack on World Trade Center. At that time, Passengers and Flight Attendants turned on the cellphones and made calls and sent messages to airlines officials and their loved ones. But, that's not the case with missing Malaysian plane.
None of the passengers or airline staff have made phone calls, sent messages or updates their social networking pages till now. Interestingly, Most of the passengers in M370 were either Malaysians or Chinese who extensively use mobiles.
Some say, The plane is flying too high to operate personal electronic devices. As per the military radar, The aircraft is flying extremely high nearly (45,000 feet which is above the certified altitude of 43,100 feet for Boeing 777-200) after taking the diversion.
On the other hand, The hijacked planes on Sept 11th, 2001 were flying very low giving an opportunity for passengers to make calls.