In this instance I'm talking about technologies that allow communication using mobile devices (usually cellular phones and PDAs).

Mass Text Messaging--if students aren't reading your emails...

• TextMarks (http://www.textmarks.com/)--text message listserv. Participants self-subscribe.
  
• TextReminder (http://textreminders.net/)--can schedule reminders to go out to different groups. Partricipants can self-subscribe.
  

Clickers--why purchase expensive clicker systems?

• PollEverywhere (http://www.polleverywhere.com/)--multiple choice and full text response options. Can embed poll and results elsewhere.
  

Audio Recording--get students to reflect their learning in a different modality.

• Gabcast (http://gabcast.com/)--no longer free to call in from a phone. Can leave text comments on each episode.
  
• drop.io (http://drop.io/)--can call in and leave audio files; however, can also upload other types of files from a computer. Can leave text comments on individual posts.
  

MoBlogging

• Utterli (http://www.utterli.com/)--upload text, audio, images, and video and then easily embed elsewhere.
  
• Posterous (http://posterous.com/)--upload text, images, & video.