Every professor I've ever had made special note in the syllabus that cell phones were to be turned off during class. If you have a situation going on where you might need to be contacted during class time, set it to vibrate and leave the class if you get a call. No texting during class.
Every single one.
I even had professors who would answer a student's phone during class time.
Despite this, I had one class where a student texted all during class. I'm not sure the prof ever noticed, but I sure did. That and the fact that she always took her shoes off was very distracting.
Seriously, what is so important that you can't wait until class is over to tell someone? I only ever used my phone if I was going to be somewhere other than where I was usually when it was time for my Mom to pick me up.
There's also the potential of cheating. Students would text answers to friends or take photos of the test and pass them around.
Personally, I get along just fine without a cell phone now.