There are a lot of free sms gateway SW in the network that you can download and use them free of charge. In most cases you need to coonect your phone to the computer or use a special device that support SMS and cellular networks.

Here is some of the FREE sms gateway Tool.

SMS Gateway by GPA Technology. v12 (32 Bit) – Trial version

For download the update version press here

SMS Gateway by GPA Technology. v12 Win7 (64 Bit) – Trial version

For download the update version press here