To choose a voice for an AgentLine phone agent, read GET /v1/voices and set voice_id on the agent. For one outbound call, pass voice_id to POST /v1/calls. The override order is call, agent, account default, then system default. A saved agent voice therefore takes precedence over a changed account default.
Read the available voices first
The public catalog returns voices with preset_name, voice_id, name and description, plus default_voice_id. Use the live catalog as the authority rather than copying a voice UUID from an old tutorial.
curl --fail-with-body https://api.agentline.cloud/v1/voices
On October 18, 2026, the catalog listed female-1 (Friendly Female), female-2 (Reassuring Female), female-3 (Guide Female), male-1 (Supportive Male), male-2 (Thinker Male), and male-3 (Helpful Male). These labels describe presets, not measured quality or suitability for every accent or language.
Save a voice on your agent
The following examples use Bash. Set AGENTLINE_API_KEY privately in your shell and replace AGENT_ID with an agent you own. This update changes the voice for subsequent calls; it does not start a call.
curl --fail-with-body -X PATCH https://api.agentline.cloud/v1/agents/AGENT_ID -H "Authorization: Bearer $AGENTLINE_API_KEY" -H "Content-Type: application/json" -d '{"voice_id":"female-2"}'To change the account fallback, PATCH /v1/account/voice with the same voice_id body. GET /v1/account/voice reads that setting. An explicit voice saved on an agent still wins. Invalid preset names or malformed voice UUIDs can produce a validation error; re-read the catalog before retrying.
Compare two voices on your own phone
Provision a number using the API walkthrough, then replace TEST_PHONE with your own E.164 number. This request places a paid call. Keep the prompt and greeting identical between tests so you are comparing voices rather than scripts.
curl --fail-with-body -X POST https://api.agentline.cloud/v1/calls -H "Authorization: Bearer $AGENTLINE_API_KEY" -H "Content-Type: application/json" -d '{"agent_id":"AGENT_ID","to_number":"TEST_PHONE","voice_id":"male-1","initial_greeting":"Hello, this is an AI voice test. Please say a time and a street name."}'Record the call ID, preset, prompt version and observations. Check pronunciation of names, dates and numbers, interruption handling, and whether short replies remain intelligible over an actual telephone connection. Read GET /v1/calls/{call_id} and its transcript after the call. A successful configuration response alone does not prove how the voice sounded to the listener.
AgentLine and Vapi configuration
AgentLine exposes a voice_id field with a hosted preset catalog. Vapi's voice documentation describes a voice object with provider and voiceId, which suits developers choosing among voice providers. Do not copy a Vapi voice identifier into AgentLine and assume it names the same voice. Choose based on the control you need, then test your actual language and call conditions.
Reviewed against AgentLine API schema and agent skill. For the rest of the calling stack, see the voice-calling guide.