The SMS triggers a relay call service to the emergency services
Trials are under way of a UK service allowing people to contact emergency services by text message.
The system is aimed at people who cannot make normal voice calls to the 999 service due to disability.
The service sends the text to a voice relay assistant, who then speaks the text message to the emergency service and then texts back their reply.
If successful, the government initiative, which is backed by Ofcom, would become permanent in early 2010.
The scheme is a joint venture between various UK telecom firms.
The live trial involves people sending text messages in a real emergency. Administrators are looking for several thousand volunteers, with a preference for disabled users.
In an emergency, the user sends an SMS, spelling out the emergency service required, the nature of the emergency, and the location.
A receipt text is then sent, letting the user know the message is being acted upon and then further texts, with instructions or questions from the emergency services, are sent as needed.
People can register for the system by texting the word "register" to 999; without registering people who send a text message to 999 will receive an automated reply saying that they are not registered.