Turn off your cell phone before class starts, or study your cell phone user manual to find out how to turn the ringer off. Each cell phone is different. Make sure the cell phone is muted during all functions. Some cell phones beep when you get a text message, voice mail, or for an alarm, even if the ringer is turned off.
Accept calls or return text messages only when a natural break occurs during class. This happens when the teacher pauses or announces a break. Only return calls if they are urgent and can't wait until the end of class. Consider others, and don't be a distraction using your cell phone.
Excuse yourself from the class and take an urgent call in the hallway. Do this only in an absolute emergency or if you are dealing with time sensitive problems.