What Is Retell AI? AI Phone Agent Pricing, Your Own Number via SIP, Turkish, n8n and KVKK

When the business phone rings, an AI agent picks up: it answers frequently asked questions, asks for a suitable appointment time and, if needed, transfers the call to a staff member. When the call ends, a summary and the fields you define (name, request, appointment time and so on) are extracted automatically and sent to your system.

Who it's for: businesses that get lots of questions and appointment requests by phone (clinics, repair services, real estate, schools) and the agencies that set them up. The agent can be built in the dashboard without code; connecting the phone line and setting up the automation take technical knowledge.

Where it fits in DijiKoçum packages: the “inbound call voice agent” add-on module of the Business Communication Package (answers the business's landline or 0850 line — Turkey's nationwide business number — handles FAQs and appointments, transfers to a human, sends the end-of-call report to n8n) and an optional module in the Appointment package.

Three parts work together: transcription (turns speech into text, STT), the language model (decides what to say) and speech synthesis (turns text into voice, TTS). Retell combines them in a single agent; you choose which language model and which voice to use.

An agent is built in one of two ways: with a single system prompt (single/multi prompt) or with a flow made of nodes (conversation flow). Retell's own documentation recommends these two for most agents; connecting your own language model server (custom LLM) is also possible, but testing and maintenance are on you.

1. 1Create an account Sign up for free at retellai.com. New accounts get a one-time $10 trial credit; it isn't given twice for the same email.
2. 2Create an agent Start from a template or from scratch; choose Turkish (tr-TR) as the language, pick a Turkish voice and a language model; decide who speaks first.
3. 3Add tools Set the human handoff number with Transfer Call and the n8n webhook URL with Custom function.
4. 4Test in the browser Try the conversation with web calls and simulation tests; voice tests are billed at the normal per-minute rate.
5. 5Connect the number Import your carrier line with Phone Numbers › + › Connect to your number via SIP trunking (see the section below).
6. 6Set up the report Enter the webhook URL and the Post Call Extraction fields; choose the Data Storage and Retention setting.
7. 7Payment and verification After the trial, add a card via Stripe. Outbound calls, buying numbers and SMS require KYC identity verification (83 countries supported).

!Payment and credit are tied to the workspace: in a second workspace you need to add the card again. Whether Turkey is on the KYC list is not stated in the documentation; check in the dashboard, and if it isn't listed, contact Retell support.

Retell sells only US and Canadian numbers. For your landline or 0850 number in Turkey, you get a SIP trunk from your carrier (such as NetGSM or Verimor): a virtual line that connects your phone line to another system over the internet. When you connect your own line, Retell charges no per-minute telephony fee and no number fee; your carrier's fees are separate.

1. 1Inbound calls (origination) In your carrier's panel, point the number's SIP routing to Retell's address: sip:sip.retellai.com (TCP recommended; UDP and TLS also available).
2. 2Outbound calls (termination) When importing the number into Retell, enter the termination URI from your carrier and, if any, the SIP username and password.
3. 3IP allowlist If your carrier applies IP restrictions, add Retell's IP blocks from the documentation to the allowlist; for audio, UDP 10000–65535.
4. 4Test the connection The Test SIP Connection button sends an OPTIONS request; success doesn't prove calls work, so try a real inbound and outbound call.

Supported audio codecs are PCMU, PCMA and G.722. When transferring a call to a human, cold transfer uses SIP REFER; for that, REFER and transfers to external lines must be enabled at the carrier. Warm transfer is done with SIP DIAL.

How to get a SIP trunk and an 0850 number at NetGSM →

If your carrier doesn't support elastic SIP trunking, the second route is “Dial to SIP URI”: you route the call to Retell with your own system. On this route Retell's transfer feature doesn't work; you need to set up transfers yourself.

This section is not an official source; it is the method followed in DijiKoçum setups. Retell's own prompting guide also recommends writing short, clear, non-repetitive prompts and not patching mistakes with “don't” rules.

• Keep the system prompt short: who it is, what it does, what it doesn't do, when it transfers. A long prompt (over 4,000 tokens) also raises the per-minute cost.
• Keep the opening announcement fixed: “This call is being recorded; I'm X's AI assistant.”
• Always keep human handoff on: a caller who says “I want to talk to a staff member” or has a complaint is transferred without being kept waiting.
• Don't bake information like appointments and prices into the prompt; read it live from the calendar and price list via an n8n webhook.
• Don't collect information such as health details or card numbers over the phone; if needed, turn on the personal data removal (PII) setting.

No subscription, no platform fee: you pay only for the minutes spoken. The official range for a voice agent is $0.07–$0.31 per minute. The per-minute cost is the sum of the components you choose. Prices are in dollars; whether VAT applies is not stated on the pricing page.

The example from the calculator on the pricing page: language model 0.04 + voice infrastructure 0.055 + speech synthesis 0.015 + telephony 0 = $0.11 per minute. Duration is billed by the second; silence and hold time are also charged, and calls that don't connect are not billed. If the agent speaks first, calls under 10 seconds count as 10 seconds.

Bring your own key (BYOK): an option to enter your own key for the language model, voice or transcription provider in Retell and pay that item to the provider directly is not listed on the official pricing page. Connecting your own language model server (custom LLM) is available; in that case, how the language model item is billed is not clear in the official documentation.

Official pricing page last checked on October 28, 2026.

The documentation says a language must be supported by both the speech synthesis and the transcription provider, and that valid combinations are shown in the dashboard's language picker. In ElevenLabs, Turkish isn't available on every model: don't pick an English-only model. Choose based on Turkish speech quality by listening to the voice samples yourself.

!If you'll make outbound (campaign) calls: in Turkey, Law No. 6563 treats commercial messages sent by phone, call center or automated dialing machine as “commercial electronic messages” and requires prior consent; İYS (Turkey's commercial message consent registry) keeps consent for the call channel separately. Messages can be sent to tradespeople and merchants without consent. Retell's terms also leave it to the customer to obtain the consent required for calls and document it for at least 5 years. Answering inbound calls is not covered by this.

Retell AINo monthly fee, $0.07–$0.31/min; 20 concurrent calls included; no telephony fee on your own SIP line; warm transfer also works over SIP.Vapi$0.05/min platform + provider costs; with your own keys you pay providers directly; 4 concurrent calls included; EU region only on Premier.

Differences according to the documentation: Retell quotes the per-minute price as a bundle, while Vapi passes on each item separately at the provider's price and accepts your own API keys. Retell keeps data in the US; Vapi defaults to the US, with an EU region on the top package. Both offer Turkish voices and transcription, SIP trunking, webhooks and n8n integration.