Bind an agent to a number, control the calls
Give an AI agent one of your carrier numbers and it answers inbound calls and places outbound ones, all from code. Each number is isolated, so you can hand every customer their own line backed by a shared agent. One REST API, flat $0.08 a minute.
Binding is the whole setup
Traditional telephony makes you wire a call flow before a number does anything useful. Here the setup is one step: attach a number to an agent. From that moment the number is a working phone line in both directions, answering callers with the agent and ready to place calls on your command. There is no flow to design and no state machine to maintain.
curl -X POST https://api.nixflex.com/v1/phone-numbers \
-H "Authorization: Bearer nxf_live:nxfs_live" \
-d '{ "phone_number": "+44...", "agent_id": "agent_8fk2" }'Both directions, one agent
Callers reach the bound number and the agent answers on the first ring: understanding, booking, routing, or transferring to a person when needed. No phone tree, whatever the volume.
Place a call from the same number with POST /v1/calls/outbound, or a whole list with /v1/calls/batch. Voicemail is handled and a result comes back per call.
A number per customer, cleanly isolated
The reason this API is safe to build a product on is isolation. Each number carries its own configuration and its own call records, so numbers never share a pool and one customer's calls never bleed into another's. Give every customer a dedicated number, back them all with a shared agent template, and manage the whole estate from one API key. That is how one agent serves two hundred clinic numbers without two hundred agents to maintain.
Every call reports back
Inbound or outbound, each finished call returns a transcript, a summary and a sentiment score, pushed to your webhook as call.ended or pulled from GET /v1/calls. During a call the agent can reach into your systems through custom functions, so it acts on live data rather than only what is in its prompt.
See the Voice AI API, Multi-tenant and Webhooks pages, or the full docs. Coming from another platform? Nixflex is a modern alternative to Retell, Vapi and Bland. Compare them →
Developer FAQ
How do I give an agent a phone number?
Create the agent, then attach one of your own carrier numbers to it with a POST to /v1/phone-numbers. The moment the number is bound, the agent answers inbound calls on it, and you can place outbound calls from it. Binding is the whole setup; there is no separate call-flow to wire.
Does one agent handle both inbound and outbound?
Yes. A bound number works in both directions with the same agent: it answers calls that come in, and you place calls out from it through /v1/calls/outbound. Both directions produce the same events and the same call records, so your integration treats them the same way.
What is per-number isolation and why does it matter?
Each number carries its own configuration and its own call records, rather than sharing one pool. That means you can give every customer their own dedicated number, backed by a shared agent template, and keep their calls and data cleanly separated. It is what makes the API safe to build a multi-tenant product on.
Can I run one agent across many numbers?
Yes, and this is the core model. An agent is a template with one personality and prompt, and it attaches to unlimited numbers. A single dental agent answers across two hundred separate clinic numbers today, each isolated, all managed from one API key.
How do I place an outbound call?
POST to /v1/calls/outbound with the agent, the number to dial, and the number to call from. For volume, /v1/calls/batch takes a whole list. Voicemail is handled, and a result is returned per call with a transcript and summary.
How do I get the result of a call?
Register a webhook to receive call.ended with the transcript, summary and sentiment the moment a call finishes, or pull any call from GET /v1/calls. During a call, the agent can also reach into your own systems through custom functions.
What does it cost?
A flat $0.08 per minute of voice, pay-as-you-go, premium model included, with your own carrier underneath. No credits, no per-number platform fee, and number charges stay on your own carrier account.
Give your agent a number today
Bind a number, answer inbound, place outbound. One API key, per-customer isolation.