I always get my students' e-mails and will occasionally send them a message. It is frustrating that half of them never check. In fact even after they e-mail me, they don't look for a reply. But here is a way to use cell phones, but not in the classroom. You could set up a database with their cell phone numbers and then add the code below depending on their cell phone and then they will receive a text. Certainly this way the kids will get the message. (Obviously this is one you'd want to check with the parents first to make sure they don't mind)
[10DigitNumber]@mobile.mycingular.comJust replace [10DigitNumber] with the ten digit phone number you are trying to reach (area+ local number).