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What is SMS Testing?

SMS testing allows you to test scenarios where your voice agent sends or receives text messages during phone calls. This is useful for testing:
  • OTP (One-Time Password) verification
  • Sending confirmation codes or links
  • Receiving information via text during a call
  • Multi-channel communication workflows

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How SMS Testing Works

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Two-Way SMS Communication

During a test call: Testing Agent (Evaluator) can:
  • Send SMS to the main agent
  • Receive SMS from the main agent
Main Agent can:
  • Receive SMS from the testing agent during the call
  • Send SMS to the testing agent
Important: SMS messages can only be received if sent to/from the same phone number being used in the active call. This ensures messages are correctly associated with the ongoing conversation.

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Enabling the Send SMS Tool

To enable SMS functionality for your testing agents:
1

Navigate to Your Agent

Go to your Agents section and select the agent you want to test.
2

Access Evaluators

Click on the Evaluators tab and select the evaluator you want to configure.
3

Enable Send SMS Tool

Scroll to the Tools section, find Send SMS in the list of available tools, and toggle the switch to enable it.
SMS Tool Configuration

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Available Testing Tools

When configuring your evaluator, you have access to these tools:
ToolDescription
DTMFSend DTMF tones during the call
End CallEnd the call at any point during the conversation
End Call Only on TransferEnd call only when a transfer occurs
Send SMSSend SMS messages during the call

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Example: OTP Verification

Here’s a simple example of testing an agent that sends verification codes via SMS. Evaluator Instructions: 
Call to update your policy information. When the agent sends you
a verification code via SMS, read the code back to verify your identity.
Test Flow:
  1. Testing agent calls and requests to update policy
  2. Main agent says: “I’ll send you a verification code”
  3. Main agent sends SMS with OTP code
  4. Testing agent receives the SMS and reads the code
  5. Main agent verifies the code and proceeds

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How SMS Appears in Transcripts

When an SMS is sent during the call, it appears in the transcript as a Function Call:
SMS in Transcript
As shown above:
  • The Function Call section shows send_sms with the message content
  • The Function Call Result confirms the SMS was sent
  • This helps you track all SMS activity during the test

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How Main Agents Handle SMS

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Receiving SMS

When your main agent receives an SMS during a call, the message is automatically:
  1. Injected into the LLM context as: [User SMS]: <message content>
  2. Added to the transcript for your review
  3. Available for the agent to use in its response

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Sending SMS

Your main agent can send SMS when configured with SMS capabilities. The SMS will appear in the transcript as a function call, just like in the example above.
Best Practice: SMS should only be sent when explicitly needed (verification codes, links, critical information). Don’t send SMS for regular conversation responses.

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SMS Filtering

SMS messages are only delivered to the active call when:
  1. Sent to/from the call’s phone number
  2. There’s an active call session
  3. The direction is correct (user ↔ agent)
This ensures SMS messages are correctly associated with ongoing calls and don’t interfere with other tests.

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Best Practices

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1. Enable Selectively

Only enable the Send SMS tool for evaluators that need to test SMS functionality.

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2. Clear Instructions

Be explicit about SMS expectations in your evaluator instructions: 
✅ Good: "Wait for SMS with verification code, then read the 6-digit code aloud"
❌ Vague: "Handle SMS messages appropriately"

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3. Validate Content

Use metrics to verify SMS messages contain correct information (codes, links, data).

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4. Check Transcripts

Review the Function Call sections in transcripts to confirm SMS was sent/received correctly.

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Next Steps