i want to know how to send sms from a java program, so far i am aware that you will need a sms gateway, but i dont know from at which point to start coding .... i am an absolute beginner, and i please help me with step by step instructions ..

:( thanx in advance

That depends on your SMS Gateway which is also, in messaging terminology, called SMSC or Short Message Service Centre. If your provider uses the HTTP Protocol to have sms sent over to them then you would need to use HTTP POST/GET method. On the other hand if your provider uses the SMPP (Short Message Peer to Peer) Protocol you would have to use the same to connect to them. Then you would become an ESME (Extended Short Messaging Entity) which can be termed as a client and the SMSC acts as the server.
In this case your communication would be through the SMPP Protocol PDUs. You can find out more about the SMPP Protocol on the net. To do this you would require a Java SMPP API using which you can communicate with the SMPP Server. One of the popular Java SMPP Libraries is here. Download it, it comes with the Java Docs. Reading SMPP Protocol Specification would also prove to be helpful.

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