Found in Wired News, this piece, No Wrong Answer: Click It, about the growing use of instant response devices in class. It includes this:
Many colleges already use technology that allows teachers and students to interact more easily outside the classroom. For example, professors can now post lecture notes, quizzes and reading lists online. Several companies market software, such as Blackboard and Web CT, that provide ready-made course web pages and other course management tools.
Mazur envisions students someday using their laptops, cell phones or other internet-ready devices for more interactivity than clickers offer. At least one company, Option Technologies Interactive, based in Orlando, Florida, markets software that allows any student with a handheld wireless device or laptop to log onto a website and answer questions, just as they would with a clicker.
How practical might it be to link in the mobile phones that so many students carry? Intensive use would probably carry a prohibitive cost but occasional use might be easier than having to provide students with an additional gizmo.