Turn off your cell phone
Unless you are expecting an important call or text, the proper thing to do is turn your cell phone completety off as soon as your enter class some students switch to vibrate mode, but sometimes this mode can be worse than a ring tone because of the intensity of yhe vibration. Certainly never answer your cell phone in class, nor text if your phone does ring, make a quick apology as you send the call to voicemail -- and then send a quick email to your professor after class apologizing for you gaffe