How can we test multiple outbound PSTN calls during development using Azure Communication Services?

Question

How can we test multiple outbound PSTN calls during development using Azure Communication Services?

Mian Omair 0

We're developing an AI-powered orchestration engine for healthcare communication at Medical Guardian. The system is designed to initiate outbound voice calls using Azure Communication Services (ACS), integrated with Azure Functions, Azure Speech Services (TTS), and FastAPI. These calls play personalized messages to patients for healthcare coordination tasks like flu shot reminders.

During development, we need to frequently test outbound PSTN calls to a single developer-owned test number to verify TTS synthesis, event callbacks, and call flows.

However, we noticed that the ACS number appears to restrict the number of outbound calls to just 2 per recipient, which limits our ability to test the pipeline iteratively.

Question:

Is there a recommended way to test ACS outbound calling workflows without hitting call limits during development?

Are there sandbox/test environments, exemptions for verified test numbers, or best practices to simulate or repeat test calls without violating trial restrictions?

Bhargavi Naragani 3,165 Reputation points Microsoft External Staff

2025-04-24T02:45:51.9766667+00:00
Hi @Mian Omair ,

To test multiple outbound PSTN calls during development using Azure Communication Services (ACS), you may face limitations with the trial phone number, which restricts outbound calls to a maximum of 2 per recipient. Unfortunately, the context does not provide specific recommendations for bypassing these restrictions or for sandbox environments.

However, here are some general best practices you might consider:

Azure provides a tool called Try Phone Calling within the Azure portal. This allows you to make test calls to verify your telephony connection configurations without needing to write any code. It could be a good way to validate your setup between more in-depth tests.

Here's how you can access it:

Go to the Azure portal and search for "Try Phone Calling."

Enter a test phone number (which can be your developer-owned number), select a caller ID, and make calls directly from the portal.

If you haven't already, consider setting up a dedicated testing environment. By using separate ACS resources, you can acquire additional trial phone numbers to distribute your tests across them.

While you’re limited to how many calls you can make to a single number, you can simulate calls by logging events and responses within your system. This won't replace live tests but can help you to refine the logic and events handling. If possible, you may want to consider batching your calls or organizing them in a manner where you can run them in cycles to avoid hitting the limits too quickly.

Stay up to date with Azure Communication Services documentation, as they often release updates and new features which might include options that can help with your scenario.

Frequently asked questions about trial phone numbers in Azure Communication Services

Try Phone Calling

Hope this information is helpful, let me know if you have any further queries.

1 answer

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Bhargavi Naragani 3,165 Reputation points Microsoft External Staff

2025-04-24T02:45:51.9766667+00:00

Hi @Mian Omair ,

To test multiple outbound PSTN calls during development using Azure Communication Services (ACS), you may face limitations with the trial phone number, which restricts outbound calls to a maximum of 2 per recipient. Unfortunately, the context does not provide specific recommendations for bypassing these restrictions or for sandbox environments.

However, here are some general best practices you might consider:

Azure provides a tool called Try Phone Calling within the Azure portal. This allows you to make test calls to verify your telephony connection configurations without needing to write any code. It could be a good way to validate your setup between more in-depth tests.

Here's how you can access it:

Go to the Azure portal and search for "Try Phone Calling."

Enter a test phone number (which can be your developer-owned number), select a caller ID, and make calls directly from the portal.

If you haven't already, consider setting up a dedicated testing environment. By using separate ACS resources, you can acquire additional trial phone numbers to distribute your tests across them.

While you’re limited to how many calls you can make to a single number, you can simulate calls by logging events and responses within your system. This won't replace live tests but can help you to refine the logic and events handling. If possible, you may want to consider batching your calls or organizing them in a manner where you can run them in cycles to avoid hitting the limits too quickly.

Stay up to date with Azure Communication Services documentation, as they often release updates and new features which might include options that can help with your scenario.

Frequently asked questions about trial phone numbers in Azure Communication Services

Try Phone Calling

Hope this information is helpful, let me know if you have any further queries.

Answer 1

Sina Salam 19,616

Hello Mian Omair,

Welcome to the Microsoft Q&A and thank you for posting your questions here.

I understand that you are having outbound PSTN call limitations on Azure Communication Services (ACS.

Regarding your specifications and questions:

Microsoft imposes stricter limits on trial ACS resources. You can submit a request to Microsoft support to raise PSTN calling limits. This often requires justifying the use case (which you already have) and getting approval for a higher quota or production use. You can also request higher limits through Azure Support on Priority Community Support : https://learn.microsoft.com/en-us/azure/azure-portal/supportability/priority-community-support
For the followings:
1. Multiple repeated test calls: Use multiple test numbers or rotate them.
2. TTS/call flow verification: Use inbound ACS bot and local simulation (Bot Framework).
3. Sandbox simulation (future-ready): Monitor for emulator/test framework release.

I hope this is helpful! Do not hesitate to let me know if you have any other questions or clarifications.

Please don't forget to close up the thread here by upvoting and accept it as an answer if it is helpful.

Mian Omair 0 Reputation points

2025-05-02T04:26:18.54+00:00

The rotation of multiple test numbers with just 2 calls per number is an extremely limited quota to build and test the LLM->TTS and SST->LLM pipeline. Especially in cases where we have to build the logic for interruptions on events from scratch, as there is no available solution ready to use (Please refer ongoing discussion in Question: What’s the Best Way to Handle Interruptions in Azure Communication Services?)

We kindly request an enhanced quota for the trial number, allowing up to 600 calls. The quota has been exhausted, and now when we create a new ACS service, it shows the attached error message: "Unable to access trial phone numbers right now. Please try again later." Without the capacity to make test calls to at least one developer number, we cannot proceed to develop the solution and have now hit a brick wall due to the limitation of calls.

Note: We are trying to build an end-to-end voice AI automation pipeline for a healthcare provider using Azure-native components. The solution will be agentic, with AI agents orchestrating healthcare workflows in the future—leveraging Azure Communication Services (ACS), Azure Cognitive Services (TTS/STT), and Azure AI Foundry (LLMs or orchestration agents). This could be a great use case for Microsoft's Azure capability as we might be the first to build this with native Azure components. But we need support from Microsoft.

Thank you for your understanding and support.

Best regards,

Mian Omair

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How can we test multiple outbound PSTN calls during development using Azure Communication Services?

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