Using cellphones in the Classroom
Poll Everywhere is a tool that can be used both synchronously and asynchronously.
A synchronous use in in the traditional classroom, especially large classes, would be to poll students during a lecture. After presenting a segment of your lecture, take a poll to assess whether the majority of students understood what was presented. The text/quiz questions could be incorporated into a PowerPoint at specific points in the lecture. There are some students who would be more likely to answer via a text than exposing themselves in the classroom. As long as you have a strict rule about when phones are out and when they are put away I do not think they would be a distraction.
I also think Survey Monkey would also be great asynchronous tool.
The tool could be used asynchronously in an online course by have the students respond to a poll by a specific due date.
I have found that most of my students have much larger text packages than minutes on their cellphones. There are a number of very inexpensive unlimited services available now. Making sure your student population has a plan that would facilitate using this technology is something one would need to be sure of before requiring excessive use of texting in coursework.