The cell phone is ubiquitous among students. Most of us have them now, too. It has become our primary and most immediate means of communication.
The fact that nearly all students have cell phones is an advantage. We can alert students to urgent situations, like campus dangers, snow days, etc. Students can maintain contact with their family members like no generation before them. Text messaging allows them to network and stay in touch with their friends. Cell phones are the quickest and most direct method of communicating to students.
Cell phones also require management in the classroom. There are simple rules of etiquette expected of students. It is entirely appropriate to put in your syllabus and to make clear to them early on that cell phone ringers should be turned off when in class.
This goes for us, too. Turn 'em to vibrate in meetings and social settings. There's nothing more embarrassing or distracting than when YOUR phone goes off, especially with hokey songs or melodies at full blast. Make it a habit to turn those ringers off.
For more on cell phone guidelines, see What is Cell Phone Etiquette.