The cockpit controls are omnipotent, i.e., the cockpit members have full access to the switches, fuses and systems that can override or turn off the oxygen mask deployment. At least this has been my limited observation of the cockpit environment.
Well, the on-board oxygen supplies for the emergency passenger maks are very, very limited: Only enough for the plane to get below 10,000 feet and then use outside air. 3-6 minutes maximum - less if people are panicking or breathing heavy.
Still, many texts or phone calls can be sent in 3-4 minutes at 40,000 feet. Cell reception at 40,000 feet over the straits between the islands? Not likely very good.
The Washington plane crashed on 9-11 was much closer to the ground, and was directly over a cell-tower populated area of the Washington suburbs. So texts and phone calls could get out even from the plane after the hijacking.
Other crew oxygen masks? Not available of the co-pilot left the cockpit to use the bathroom - like the plane that a Muslim pilot crashed over Europe a few years back: The pilot was locked out of the cabin, and then the plane was flipped and dove into a mountain.