It is certainly a "feel good" moment for anyone who has ever had their time wasted by inappropriate cell phone use. I spend much of my time interviewing people, and some people leave their phones on during the interview and once in a while the phone will ring. What they do from that point forward determines my reaction. If they shut off the phone without looking at who is calling, and apologize for the indiscretion, I accept the apology and move on with the interview. Believe it or not, the odd person actually wants to take the call. I ask if it is some sort of family related emergency. If it isn't I tell them they can spend all the time they want with the call, because our interview is finished.

Assuming this was real (and I agree that it was probably a set up), the professor was wrong to break the phone. He had two better options.

1) Kick the student out of class and do not allow him to return after he completes the call. The embarassment of that would probably prevent anyone from making the same mistake.

2) If the student refuses to leave, then the professor "pulls an Axl Rose" and ends the class, explaining to the rest of the students that the actions of their classmate have resulted in them having their time wasted. Same result as option number 1, in all likelihood.