The service is referred to by different colloquialisms depending on the region.
It may simply be referred to as a "text" in North America, the United Kingdom, Australia, New Zealand and the Philippines, an "SMS" in most of mainland Europe, or an "MMS" or "SMS" in the Middle East, Africa, and Asia.
Some of the best sex portals online do require people to register however, and that is mainly to keep out the spammers and bots.
Some places require registration because they want to spam you, and we have tips for dealing with that.
Governmental and non-governmental organizations use text messaging for communication between colleagues.