I will suggest that you should use JSMPP (git page). JSMPP is the Java implementation of SMPP (Short Message Peer-to-Peer). It provides the communication channel between your web application and the SMS service center. It supports upto 5000 SMSs per second. The SMS service center will charge you for the service but you can do as much testing as you want by using
Selenium simulator. Both the JSMPP and Selenium simulator are free of cost.
It would be a great useful to future users if you add some details in the answer.Writing information in comments is not that much attractive to users