Considering you configured your VoIP Drupal with one of the providers, here is the sample code snippet that sends "Hello world" SMS:
<?php $number = '+1234567890123'; //Number to send SMS to. Must be in E.164 format. $call = new VoipCall(); $call->setDestNumber($number); $text = 'Hello from VoIP Drupal'; voip_text($text, $call); ?>
Pretty cool, right?