Unfortunately, I think there can be arguments made for allowing use of cellphones in specific circumstances. Realistically speaking, our students are going to use the calculator on their cellphone to do any math that their adult life requires, so why shouldn't we teach them with the tool they will be using? As more and more phones have internet access capabilities, should schools be teaching students how to evaluate internet sources for reliability and validity of information? Taking pictures with cellphones could serve to illustrate reports on field trip activities, document experiment outcomes, and serve many other very valid educational purposes.
The challenge is getting students to use the phones responsibly and appropriately, which means phones are not being used during lectures, to bully, to take pictures in the locker room, and so on. It may be that the only alternative is to completely ban them, but it is too bad if that's the case.