this link you can use it to send short massage system (SMS) to all operators like indosat, xl, telkomsel, three, fren, fleksi, axis, hepi, ceria, esia, etc, you can also send SMS to singapore, hongkong, prancis, etc.
even indosat im3 just rp 4/sms to all operator but we need free too, if you're always connected to the internet, below some links you can use it for sending sms:
all links is funtion well and I have already use it