Thanks for asking question! If I have understood right, you want to send SMS messages using Azure Communication Services. There is Pre-requisites, and you should have An SMS enabled telephone number.
You may refer to this Quickstart: Get a phone number using the Azure portal
Also Please Note that SMS messages can be sent to and received from United States phone numbers. Phone numbers located in other geographies are not yet supported by Communication Services SMS. For more information, see Plan your telephony and SMS solution.
To elaborate further :
- Only US is supported for purchasing phone numbers at this time. This is based on the billing address of the subscription that the
resource is associated with. At this time, you cannot move a resource to another subscription. - When a phone number is released, the phone number will not be released or able to be repurchased until the end of the billing cycle.
- When a Communication Services resource is deleted, the phone numbers associated with that resource will be automatically released at the same time.
Refer to official document link might be helpful: https://learn.microsoft.com/en-us/azure/communication-services/quickstarts/telephony-sms/send?pivots=programming-language-csharp
Let us know If you have further question on this.