Recently we have started integrating SMS (Short Message Service) into some of our online recruitment websites. This allows automated or manual SMS (text messages) to be sent to a mobile phone. This is obviously a very effective and personal way of contacting your users.
The advantage of two-way SMS is it allows the recipient to respond to the message in the normal way and for the website to then get updated respectively. An example would be an admin could click a link on there website to see if another user is free on Wednesday, this would then instantly send a SMS to the user in question's mobile phone. The user could then reply to the SMS which would then get sent back to the website and update the admins list of who is and who is not available on Wednesday. Alternatively we could email the admin the response.