SMS
SMS allows you to send a short text message (up to 160 characters) from one mobile phone to another mobile phone. If you have never created a text message then the VideoJug tutorial will help. It looks at entering text on the keyboard, predictive text and the use of initialisations and emoticons.
VideoJug -How To Text MessageSMS
SMS without a mobile phone
Ipipi is a service that allows you to send text messages from a computer. Web SMS and TalkWeb provide a similar service.
SMS - delivery to many
A bulk SMS gateway such as Bulk SMS or Mediaburst provide a service of one message delivered to many people in a list.
XLearn offers 2-way text messaging - and a text wall - to provide a push and pull service from learners to tutors, all of which can be managed online.
How to send an SMS from an ITouch
Web 2.0 options
Microblogs
Twitter is a microblogging tool that allows you to send free short messages of 140 character length between friends and colleagues.
Yahoo email to SMS
Yahoo has an e-mail service that sends SMS. The text messaging feature is integrated into the interface and works in almost exactly the same way as standard emailing, but users enter a phone number instead of an email address. Each message is limited to 150 characters.