Clearstream - Clearstream is a SMS marketing and online texting software.
Jasmin SMS Gateway - Jasmin is a very complete open source SMS Gateway with many enterprise-class features such as:
Swift SMS Gateway - SMS Gateway is your bridge between the Internet and the world of cell phone SMS text messaging.
Kannel - Open Source WAP and SMS Gateway
Maytapi - Serverless Whatsapp Api with Chat and Agent support.
Bulk SMS Services - Sending Bulk SMS to the customers will engage the customers with your business and new offers.