Edit: Damnit, Adrenalynn beat me to it, lol.
Some casinos where I am do have a jammer that disables certain electronic
devices in sensitive areas as well. But for the most part, they just keep an eye on you. It's not like they can take away all of your earnings regardless, if they suspect you of cheating or something. If your cellphone rings at the table, I don't think they expect you to just sit there and talk while you play the whole time, hehe. The dealer might ask you to step away from the table until you're done if they suspect anything.
I do remember that you can flash a light in the tray areas of certain slot machines to make it pay out. I'm sure they've fixed it by now, but it's amazing that a simple flashlight aimed up into the tray could set it off like that.