Instead, there is an option to use third-party tool from Twilio
AWS does provide direct API for SMS, integrated with many other services.
How to Use Twilio for Voice and SMS (.NET) | Microsoft Docs
Add the Twilio Connector in your Azure Logic apps | Microsoft Docs
Get started with the Twilio connector
How to Send Daily SMS Reminders Using C#, Azure Functions and Twilio
Voice Pricing for Phone Numbers & Calls - Twilio
ahoy.twilio.com/azure
Twilio - Wikipedia
"Twilio uses Amazon Web Services to host telephony infrastructure and provide connectivity between HTTP and the public switched telephone network (PSTN) through its APIs.[21]"
Build an SMS queueing system using Azure and 100 lines of code
SDKs - Twilio
The Twilio C#/.NET Helper Library - Twilio
Your Cloud Buddy: Azure Notifications Hubs not equal to SMS
Azure Notification Hubs does not itself provide SMS text messaging to mobile devices.
"To send SMS text messages from Azure, for example, you can use services like Twilio which is available in the Azure Marketplace. You can use Twilio Connector as an API App (for example that you can invoke from Logic Apps) or your can use the Twilio API directly. "
Gigaom | Why Amazon Will Make or Break Twilio
Gigaom | Why Amazon Will Make or Break Twilio