Make a voice call or phone call to a given number. Accepts prompts like
AI agents invoke voice_call to trigger actions in Telephony MCP Server. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.
This tool initiates an outbound voice call via the Vonage API, which is an external real-world action with tangible effects (calling a phone number). It is not merely writing data but executing an operation that affects the outside world. Misuse could result in unwanted calls to arbitrary numbers, harassment, or abuse of telephony resources, warranting a high severity rating.
From the tool's definition 'Make a voice call or phone call to a given number' - triggers an external real-world telephony operation
Documented attack patterns abuse exactly the kind of access voice_call gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Telephony MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for voice_call:
{
"version": "1",
"default": "deny",
"tools": {
"voice_call": {
"limits": [
{
"counter": "voice_call_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}voice_call stays usable, but rate-capped — a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.
Free to start. No card required.
Make a voice call or phone call to a given number. Accepts prompts like. It is categorised as a Execute tool in the Telephony MCP Server MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the Telephony MCP Server MCP server in PolicyLayer and add a rule for voice_call: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Telephony MCP Server. Nothing to install.
voice_call is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.
Yes. Add a rate_limit block to the voice_call rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for voice_call. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
voice_call is provided by the Telephony MCP Server MCP server (khan2a/telephony-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Telephony MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
Free to start. No card required.
5 Telephony MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.