SMSin is an application that can send SMS for free to a few operators in Indonesia via internet connection.

Some of the features:
- Does not require phone credit (use internet connection)
- Fast SMS delivery
- Easy to use
- There is an "Inbox" feature
- There is an "Outbox" feature

Note: This app sends SMS using a random number so you need to include your name at the end of the SMS so the recipient understands that it is your SMS.