According to the Washington Post, the phones of the passengers and crew appeared to be functioning after the plane disappeared:
One of the most eerie rumors came after a few relatives said they were able to call the cellphones of their loved ones or find them on a Chinese instant messenger service called QQ that indicated that their phones were still somehow online.
A migrant worker in the room said that several other workers from his company were on the plane, including his brother-in-law. Among them, the QQ accounts of three still showed that they were online, he said Sunday afternoon.
Adding to the mystery, other relatives in the room said that when they dialed some passengers’ numbers, they seemed to get ringing tones on the other side even though the calls were not picked up.
The phantom calls triggered a new level of desperation and anger for some. They tried repeatedly Sunday and Monday to ask airline and police officials about the ringing calls and QQ accounts. However unlikely it was, many thought the phones might still be on, and that if authorities just tracked them down, their relatives might be found. But they were largely ignored.
According to Singapore’s Strait Times, a Malaysia Airlines official, Hugh Dunleavy, told families that the company had tried calling mobile phones of crew members as well and that they had also rang. The company turned over those phone numbers to Chinese authorities.