Recently I have been approached by two lecturers to discuss the possibility of using Bulk SMS to communicate with students. Bulk SMS portals such as http://www.bulksmsportal.co.za offer SMS packages at a comparatively cheap rate (e.g. R0.27 for a bundle of 500 SMS). You can pay via Credit Card, direct deposits or electronic transfers. These portals allow you to import student cell phone numbers via an Excel spreadsheet and link these students to specific groups, which makes it easy to send out an SMS to a large group of students.
BulkSMSing is great if you need to reach your students quickly, especially if they are not on campus. They can reply to the SMS (but have to pay for that SMS from their own pocket). You will receive their responses either by phone or by email.
An example on how BulkSMS are going to be used at CPUT: Estelle Buys, lecturer in the Department of Food Technology, who is responsible for the work-integrated learning course, is planning to communicate with her students via BulkSMS during their work placements.
If you would like to try it out, http://www.bulksmsportal.co.za gives you 10 SMS for free to play around with.