If you’re strictly looking for free SMS apis, I would check out this API collection, which contains SMS APIs that are free, have a freemium pricing model, or offer a free trial credit
SMS APIs Breakdown
In today’s digital world, there is no doubt that innovation is changing our conventional ways of doing things.
The business environment has experienced tremendous technological change over the years.
In order to remain competitive, one must adapt to the new ways of selling products and services, such as integrating with an API for sending SMS messages.
8 Best SMS API to Send Message to Your Users