To use a dorky Star Trek analogy, the characters on these shows use their communicators, the 24th-century version of cell phones, either only in dire situations or for absolutely necessary communication. Maybe I'll just replicate myself a cheeseburger. Boy, it's hot down here. I'll see you in a minute.
Cell phones can be great tools.
The other weekend I was sitting in a NYC park and some old drunk bastard started waving a giant knife around. In about 2 seconds, at least 2 dozen people whipped out their cell phone and quickly dialed 911. I felt more sorry for him than threatened for my life. That didn't prevent 3 cop cars from showing up in about a minute, however. Or, outside of the city, I find it horrific that there actually has to be laws written to tell people not to chat on the phone while driving.