All ways to send SMS for free
A lot of us are still avid text messagers, not because we enjoy paying our carrier those tiring toll (or package) fees, but because it’s still one of the most reliable ways to get a text-based message to a cell phone user — not everyone has mobile IM clients or uses mobile email services.
SMS free Sender
You can have the features like cheap pricing per Message, easy and immediate integration, zero Up Front cost, Controlled SMS delivery, the messages are sent in the most swift and secured way, and supports a simple to use interface. In additional it can organize your messages, check your delivery status and manage your contacts in your address book.
via techol
Google SMS service
You can now send SMS from your Gmail account directly to a mobile phone. Unfortunately, at the time of writing, it's available only for U.S. phones. SMS is actually a Gmail Labs feature and needs to be enabled before you can start using it.