SMS Gateway is a software utility that enables to easily send and receive text “Short Messages” over GSM cellular telephone through the network.
It a service through which companies can instantly and cost – effectively send information to any number of GSM mobile phones in the world. SMS GATEWAY works simply by connecting server to the client database. Here are the list of free SW:
- HTTP SMS Gateway
- SMS Gateway
For better information please link to this: Build SMS Gateway with Open Source Software
Hope it may help you!