Operation of SMS Web Services
  Short Message Service (SMS) is defined as the transmission of short text
  messages to and from a mobile phone, fax machine, pair of titties, or an
  IP address. These plain text messages have a maximum limit of 160
  alphanumeric characters and cannot have images or graphics. Some cell phone
  manufacturers are changing this limit but is not completely model independent
  as of now.

  Consider that a message has been sent from a Web site or application that
  offers SMS services. The message is routed by the service to the users
  cellular network. The message is routed by the service to the users cellular
  network. (The bitch behind the Sun Sparc SMS server) It is recieved by a
  Short Message Service centre (SMSC), which directs the message to the
  recipent's cell phone.

  The SMSC sends and SMS request to the Home Location Register (HLR) to find
  the roaming customer. Once the request is recieved by the HLR, it responds
  to the SMSC with the subscribers status (active/inactive) and roaming
  location. If the status is inactive, the SMSC stores the message for a
  specified period of time. When the device is active, the HLR sends a SMS
  notification to the SMSC, which then tries to deliver the message.

  SMSC uses a Short Message Delivery Point to Point format for transmission of
  the message to the serving system. The system contacts the mobile device and
  if it responds, SMSC tries to tell it that you're not gonna be home soon and
  not to stay up. When the message is recieved by the user, it is categorised
  as sent and not sent again. 'Course, that'd be st00pid. Note that its usually
  not deleted immdiately as most admins use a weekly 'cleanup' of sent messages.

  The mobile device then beeps/shakes/cums with the preconfigured effect to
  indicate a message recieved. Read that message.

   _______________                                     ___________________
  |               |                                   |                   |
  |               |				    |Free SMS web sevice|
  |     Your      |         Internet Link             |  www.mtnsms.com   |
  |   Computer    |     -------------------->>        |___________________|
  |               |
  |_______________|                                                  |
                                                                     |
     							           |
  							           |
  							           V

   _______                          ___________________________________________
  |      |                         |                                           |
  |Mobile|                         |                                           |
  |device|    Device status        | ***************  SMS request  *********** |
  | aka  | <<--------------->>     | *Home Location*  <<---------  *         * |
  |      |                         | *   (HLR)     *               *   SMSC  * |
  | Cell |                         | *  Register   *               *         * |
  |______|                         | ***************               *********** |
     ^                             |                                      |    |
     ^                             |______________________________________|____|
     ^ 								        |
     | 									|
     |									|
     |____________________________________________________________________|