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
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.,
Digimiles - Digimiles is A2P messaging platform that enables startups, SMEs, businesses and corporate's to market their products and interact with their customers 24/7 effectively.
Power SMPP - Enterprise grade messaging software