Jasmin SMS Gateway - Jasmin is a very complete open source SMS Gateway with many enterprise-class features such as:
Clearstream - Clearstream is a SMS marketing and online texting software.
Kannel - Open Source WAP and SMS Gateway
E-goi - Email Marketing companies, SMS Marketing, software email marketing.
Bulk SMS Services - Sending Bulk SMS to the customers will engage the customers with your business and new offers.
Maytapi - Serverless Whatsapp Api with Chat and Agent support.