The development of technologies, including computer science, has stimulated the emergence of new forms of communication between speakers through machines. Some of these new forms only involve writing, such as in SMS and chat communication. In only one decade, this Computer-Mediated Communication (CMC), as we call it now, became an established phenomenon among young people all over the world. It would be hard to ignore the time one spends chatting on the Web or "typing" on the keypad. The predominance of these practices raises questions on their impact on the communication forms used by younger generations. Thanks to the international sms4science project, we have at our disposal an important French corpus of 50.000 messages and the profiles of their authors. This corpus is the basis of our study of variation. We look at the differences of SMS practices between regions, age, sex, educational level, notably when you consider phenomena such as neologisms, question marking, spelling, negation or regionalisms. Is there always a tendency to abbreviate words and sentences? How can we call and define this practice? We try to find answers to these questions in our thesis.