Jasmin SMS Gateway - Jasmin is a very complete open source SMS Gateway with many enterprise-class features such as:
Kannel - Open Source WAP and SMS Gateway
Power SMPP - Enterprise grade messaging software
Bulk SMS Services - Sending Bulk SMS to the customers will engage the customers with your business and new offers.
KAPSYSTEM - KAP Computer Solutions Pvt. Ltd.,
Twilio - Brings voice and messaging to your web and mobile applications.