The classroom is not a place for electronic devices. Cell phones only add to the problem of students who would rather drift into off-topic conversations than learn. Studies have shown that higher cell phone use = lower grades.
Another reason why they should be banned is how they can be used to cheat. Students are able to communicate with someone else or use the internet to figure out those test answers. What if it distracts them from the actual test while they're talking to their friend in the other class? It would also distract their fellow students because of the sounds made by cell phones.
As for MP3 players, I think they should be allowed, as long as it's not while the teacher is talking. Music can help you while studying as long as it doesn't divert the student's attention (for example, music with singing is more distracting than just instrumental).
MP3 players should be allowed under some circumstances, but phones should only be used outside of school.
Although distracting during the lesson they are a good thing to use on free time. Any teacher would tell you that emotion is a good thing, and music brings out emotions. It also gives us students a way to rid the stress of every day of our lives. So yes they need to be allowed.
School isn't a place for someone to be busy with themselves. Mobile phones will distract them in class, even sometimes my friends choose to listen to their music rather than listening to the teacher's explanation. They should keep reminding themselves that parents do not pay their school fee for playing phones or listening to music. Parents pay it for them to study.
First of all, I beleive that MP3 players should be allowed regardless, since I have no problem working while listening to music. Mobile phones are different, since almost everyone has Facebook or some social app they use, which would of course distract them from their work of they choose to use this during class time.
But I think that we should let students choose to listen or not to listen, or to work or not to work (especially in the higher grades). Because prehaps when the students who use Facebook all class time get E's, they might think twice before bringing a device that's pinging them 24/7.