If we observe, at this time the service offers a lot of sms with a very cheap price to Rp. 1; per sms. There are even offering free, of course with certain conditions.
Unlike the voice calls, sending SMS is not being charged for interconnection, the term "Sender Keep All", all income became the property to the sender operator. This policy is played by the Mobile Operator.
The future, I predict will be sending SMS for free. And the income from which the service? Mobile operator will get revenue from ads that are sent or embed in the content at the end of the sms, so as Feed in Google AdSense.
Customers will be given the option, if want to SMS for free, people will be inserted ads on each SMS sent. If you want free of ads, people sending sms charged.