# Voice Call API: How to Add AI Calling to Your Applications To the customer, an AI phone call feels like a simple conversation. Behind it, four separate systems are racing to keep up with every word. A voice call API connects your app to the phone network. Then speech recognition, a language model and a voice engine take turns in a fraction of a second. If one of them lags, the whole call feels off. In India, there's a fifth piece to manage. Since September 2026, [TRAI requires app-placed calls](https://techcrunch.com/2026/09/18/india-forces-caller-id-apps-to-feed-spam-reports-to-telcos/) to be declared as A2P. Let's look at what each layer does, what it costs and how to wire it into your app. ## **TL;DR** Short on time? These are the points that matter most: - A voice call API lets software place and answer calls, and an AI layer adds an agent that talks. - Every AI call runs on four layers: telephony, speech-to-text, a language model and text-to-speech. - Speech is rarely the highest cost. Sarvam lists speech-to-text at ₹0.49 a minute, before telephony and the model. - A +91 number usually needs business KYC first, or you can connect your own carrier over SIP. - TRAI now treats app-placed calls as A2P calls, so declare them and your numbers before you scale. ## **What Is a Voice Call API, and How Is a Voice AI API Different?** Put simply, a voice call API is a set of web endpoints for starting, receiving and controlling phone calls. For years, it mostly powered OTP calls, IVR menus and masked numbers for delivery apps. A voice AI API goes a step further. It puts an agent on the line that listens and works out what the caller wants. The agent then answers in a natural voice, in real time. ### **Telephony API vs Voice AI API** Seen side by side, the difference is clear. Here is how a plain telephony API compares with a voice AI API on the points developers care about: | | **Telephony API** | **Voice AI API** | |---|---|---| | What it does | Connects and routes calls | Runs the whole conversation | | Who talks | A recording, or a person on your team | An AI agent | | What you build | IVR menus, OTP calls, number masking | Lead qualification, reminders, support | | What comes back | Call status and duration | Transcript, summary and call outcome | In practice, teams that start with a plain telephony API often bolt an AI layer on later. So if you are starting fresh, a voice call API that handles both saves you a second project. ### **The Four Layers Inside an AI Call** Under the hood, every AI phone call passes through four layers, and each one has its own job. Get any of them wrong, and callers notice straight away: - **Telephony:** puts the call on the phone network through numbers, carriers or SIP trunks. - **Speech-to-text:** turns the caller's words into text the model can work with. - **Language model:** decides what to say next, based on your prompt and the conversation so far. - **Text-to-speech:** turns that reply back into a natural-sounding voice. Some newer speech-to-speech models merge the middle steps, which can shorten the pause before each reply. Meanwhile, most of the telephony jargon you will meet comes from [cloud telephony](https://dialnexa.com/blogs/cloud-telephony-what-it-is-how-it-works-where-voice-ai-fits-in/), from SIP trunks to virtual numbers. ## **How Does a Voice Calling API Work for Outbound and Inbound AI Calls?** A voice calling API handles traffic in both directions. The mechanics differ slightly, though, so it is easier to take outbound and inbound calls one at a time. ### **Outbound: From One API Request to a Finished Call** Outbound calls follow a short, predictable path. Your app sends the number to dial, the agent to use and any useful details. The platform then dials, and the agent takes over the conversation. **Your app → POST /v1/calls → platform dials → agent talks → call ends → webhook to your server** Those extra details travel in a field called metadata. Send a customer's name and plan, for example, and the agent can greet the customer and mention the Gold plan. ### **Inbound: Pointing a Number at an Agent** Inbound is even simpler. On DialNexa, you assign a published agent to a phone number, and that agent answers every call to it. A home loan enquiry line in Jaipur could then answer eligibility questions at 11 pm. There is no keypad menu to design. ### **What Comes Back After the Call?** Once the caller hangs up, a call\_ended webhook posts the result to your server. For a completed call, the payload can include: - The full transcript of the conversation - A summary of what was agreed - A recording link, which expires after seven days - Post-call analysis, such as sentiment and intent ## **How Do You Add AI Calling to Your Application, Step by Step?** With the concepts in place, wiring up a voice call API is fairly quick. DialNexa's [API quickstart](https://dialnexa.com/docs/api-reference/quickstart) makes a good worked example, and by its own estimate it takes about ten minutes. ### **1. Pick One Call and Decide What Success Looks Like** Start narrow, even if the roadmap is big. "Call every new loan enquiry within minutes and book a callback" is a good first project. "Automate our sales calls", by contrast, is far too broad to measure. ### **2. Create and Publish an Agent** Setting up the agent takes three quick moves, and the order matters here: - **Create an API key:** you only see it once, so store it safely and send it as a Bearer token. - **Configure the agent:** pick a language and a voice, then write a short prompt. - **Publish the version:** only published versions take calls, so drafts never reach customers. ### **3. Get a Number, or Bring Your Own** Next, you need a number to call from. You can buy an Indian or US number inside DialNexa once business KYC is done. Alternatively, link a carrier you already use over SIP, as the India section below explains. ### **4. Trigger the Call From Your App** This is the part your code actually handles. You send a POST request to https://api.dialnexa.com/v1/calls with your API key and a short JSON body: { "phone\_number": "+919876543210", "agent\_id": "YOUR\_AGENT\_ID", "metadata": { "customer\_name": "customer name" } } The phone number goes in E.164 format, with the plus sign and the country code. For bulk work, batch calls take a CSV or Excel file of leads, while workflows chain several calls together. ### **5. Handle Webhooks Like Production Code** Webhooks are where integrations tend to break quietly. DialNexa signs every delivery with an x-dialnexa-signature header, so a few habits keep you safe: - Verify the HMAC-SHA256 signature against the raw request body before parsing the JSON. - Use a constant-time comparison when you check it. - Accept both keys during a secret rotation, since deliveries carry a second header for a while. ### **6. Test It Like a Real Caller** Demo calls are polite, but real callers rarely are. Before launch, put the agent through a few deliberately awkward tests: - Interrupt it mid-sentence and see whether it stops to listen. - Stay silent for ten seconds and watch how it recovers. - Switch to Hinglish halfway through, then ask outright whether it is a bot. Afterwards, listen to the recordings rather than only reading transcripts. A transcript will never show an awkward pause, but a recording always will. ## **Which Speech APIs Support Indian Languages, and What Do They Cost?** Speech is usually the first cost people check in a voice call API budget. It is rarely the biggest one, yet prices and language coverage vary a lot between providers. ### **Indian-Language Speech API Pricing at a Glance** The table below lists published prices from four providers that developers in India often compare. It also shows which Indian languages each one covers: | **Provider** | **What it offers** | **Indian languages (as published)** | **Published price** | |---|---|---|---| | Sarvam AI | Saaras speech-to-text, Bulbul text-to-speech | Indic-first; its site lists 12 Indic languages for speech-to-text and 11 for text-to-speech | Speech-to-text ₹0.49/min; text-to-speech ₹2–₹3 per 1,000 characters | | ElevenLabs | Text-to-speech, Scribe speech-to-text, Speech Engine | Hindi and Tamil on Multilingual v2 and Flash v2.5; v3 adds Bengali, Gujarati, Kannada, Malayalam, Marathi, Telugu, Urdu and more | Text-to-speech $0.04–$0.08 per 1,000 characters; Scribe $0.22/hour | | Deepgram | Real-time speech-to-text | Nova-3 Multilingual includes Hindi | $0.0058/min streaming (promotional; regular $0.0092) | | Google Cloud | Speech-to-Text V2 | Hindi, Bengali, Tamil, Telugu, Marathi, Gujarati, Kannada and Malayalam on Chirp models | $0.016/min for the first 500,000 minutes | These prices come from each provider's pricing page, checked on 22 October 2026. Note that the units differ: speech-to-text is priced by time, while text-to-speech is priced per 1,000 characters. ### **ElevenLabs API Pricing in Practice** ElevenLabs is known for natural-sounding voices, and its [API pricing](https://elevenlabs.io/pricing/api) is public. Text-to-speech costs $0.04 per 1,000 characters on Flash and Turbo, and $0.08 on Multilingual v2 and v3. To make that concrete, picture a two-minute call where the agent speaks about 1,200 characters: **1,200 characters × $0.04 to $0.08 per 1,000 ≈ $0.05 to $0.10 per call** That covers the voice alone, however. Speech-to-text, the language model and telephony all sit on top of it, which changes the total quite a bit. ### **Why the Speech Price Isn't Your Real Cost** A live AI call stacks several charges on top of each other. For most setups, the bill includes: - Telephony, for the minutes on the phone network - Speech-to-text and text-to-speech, for both sides of the conversation - The language model, for every reply it writes - The platform fee, for running the whole call That is why cost per successful outcome beats cost per minute as a measure. On DialNexa, provider costs sit on top of the [per-minute pricing](https://dialnexa.com/pricing), which is ₹5 a minute on pay-as-you-go. ## **Can a Voice Call API Use Indian Phone Numbers and SIP?** Yes to both, although each route needs some groundwork. There is also one new rule that applies to every app-placed call in India. This section is worth reading in full. ### **Indian Phone Numbers Start With KYC** To buy a +91 number on DialNexa, you first complete business KYC. Have these ready before you start: - Registration proof, such as a COI or Udyam certificate - Tax proof, such as a GST certificate or business PAN Review usually takes about one business day, and the workspace also needs a compliance ID. Until KYC clears, non-SIP batch calls can only reach the owner's registered number. ### **India SIP: Bringing Your Own Carrier** Many companies already have a telecom provider they trust. With SIP trunking, they can link that carrier to the AI platform and keep their caller ID and media path. DialNexa supports username-and-password or IP-based authentication, and its validation probe places a real test call. That probe only checks that the trunk rings. So plan your [SIP integration](https://dialnexa.com/blogs/sip-integration-for-voice-ai-a-guide-for-indian-enterprises/) carefully, and test the audio properly. ### **The TRAI Rule Every Developer Placing Calls Should Know** On 18 September 2026, TRAI's [TCCCPR (Third Amendment) Regulations](https://telecomlead.com/telecom-services/trai-tightens-spam-call-rules-with-ai-ml-detection-%E2%82%B90-05-a2p-charge-and-faster-enforcement-127804) gave A2P calls a formal definition. They are calls placed by an application, software system or automated platform, without a person dialling. That is exactly what a voice call API request does. So businesses must declare A2P calling, and the numbers they use, to their telecom operator in advance. Otherwise, those calls are treated as spam. The rule has a cost side, too. The receiving operator can charge the calling operator up to ₹0.05 per minute on A2P calls. Designated commercial number series are exempt. Treat this as a summary, not legal advice. ## **What Makes the Best Voice AI API for Outbound and Inbound Calling?** There is no single best voice AI API for outbound and inbound calling, only the best fit for your calls. Even so, four checks quickly separate strong options from weak ones. ### **Real-Time Feel** Pauses kill phone conversations, so start with latency. DialNexa's [**voice AI report**](https://dialnexa.com/blogs/state-of-ai-voice-calling-india/) covers over one million AI-assisted calls in India. It measured median response under one second, with the 95th percentile (P95) around 2.1 seconds. That is why you should ask every provider for its P95 figure, not just the average. After all, the slow moments are the ones that make callers hang up. ### **Scale and Limits** Next, find out how many calls a voice call API can run at once, and how fast you can hit it. Keep in mind that a batch of 10,000 calls is not the same as 10,000 calls at the same moment. ### **Developer Experience** Then look at the day-to-day experience of building on the API. Clear docs, signed webhooks and an honest SDK status all count for more than a polished demo. ### **Language Depth Over Language Count** Lastly, a long language list on a website proves very little. The same report found speech-to-speech models handled Hindi-English switching more consistently than step-by-step pipelines. Test the languages your users actually speak, on real phone audio. ## **What Mistakes Should You Avoid When Going Live?** Most voice call API launches that go wrong fail in the same few places. Fortunately, each one is easy to avoid once you know what to look for, and how to test for it. ### **Testing the Demo, Not the Failure Paths** Demos run on clean audio and patient callers, which is exactly why they mislead. Before launch, test no-answers, wrong numbers, voicemail, timed-out webhooks and trunks that ring but carry no audio. ### **Launching Without a Human Handoff** Some calls will always need a person, so decide in advance when the agent steps aside. A good [warm call transfer](https://dialnexa.com/blogs/what-happens-in-the-six-seconds-after-your-dialnexa-ai-agent-says-let-me-get-you-a-person/) passes along a summary, so the caller never repeats their story. ### **Measuring Volume Instead of Outcomes** Calls placed look impressive on a dashboard but say very little. Track these instead: - Connect rate and task completion - P95 latency and early drop-offs - Handoff rate and cost per successful outcome ## **How Does DialNexa's Voice Call API Fit In?** [DialNexa](https://dialnexa.com) is an enterprise voice AI platform based in Bengaluru. One REST API covers agents, calls, batch calls, workflows, phone numbers, SIP trunks and signed webhooks. It handles inbound and outbound calls alike. You also choose the stack for each agent. Speech-to-text options include Deepgram, Soniox and Sarvam Saaras, while models come from OpenAI, Google or Groq. Voices include ElevenLabs and Cartesia. Here are the numbers developers usually ask about first: - **Pricing:** ₹5 per minute on pay-as-you-go, ₹4.2 on Growth and ₹2.5 to ₹3.5 on Enterprise, with provider costs extra. - **Concurrency:** 2 calls on pay-as-you-go, temporarily up to 20; 10 on Growth, expandable to 40. - **API limits:** 150 requests per 60 seconds per key, per endpoint. - **Languages:** English, Hindi and Hinglish, plus Bengali, Gujarati, Kannada, Malayalam, Marathi, Punjabi, Tamil and Telugu, among 27 listed languages. - **Getting started:** ₹1,000 in free credits; no SDK packages yet, so you call the HTTP API directly. ## **Conclusion** Making a phone ring from your code takes minutes. Making the conversation feel natural takes more planning. Speech, numbers, webhooks and compliance all have to work together. Before you commit to a voice call API, run through a few quick checks: - Does it support Indian numbers and SIP trunks? - Can it handle Hindi, English and the mix in between? - Can you see the full cost per minute, not just one layer? - Does it hand calls to a human when the agent gets stuck? If the answer is yes across the board, start with one call flow and measure outcomes from day one. Connect rate and cost per successful call will tell you far more than the number of calls placed. ## **Frequently Asked Questions** ### **1. What Is the Best Voice AI API for Developers in India?** It depends on your calls, but a few things matter for most Indian teams. Look for Indian numbers, strong Hindi and Hinglish handling, low latency, signed webhooks and pricing in rupees. DialNexa covers these with a REST API, SIP support and pay-as-you-go pricing of ₹5 a minute. Either way, test shortlisted APIs on real callers first. ### **2. Which APIs Support Indian Languages?** Several speech providers do. Sarvam is built for Indian languages, and ElevenLabs supports Hindi, Tamil and more on newer models. Deepgram's Nova-3 Multilingual includes Hindi, and Google covers major Indian languages on Chirp models. A platform such as DialNexa then combines these into one voice call API. ### **3. How Much Do Indian-Language Speech APIs Cost?** Per minute, the published prices are low. Sarvam lists speech-to-text at ₹0.49 a minute, while ElevenLabs charges $0.04 to $0.08 per 1,000 characters for text-to-speech. However, a full AI phone call costs more, because telephony, the language model and the platform fee sit on top. So budget per successful call. ### **4. Can Voice APIs Use Indian Phone Numbers?** Yes, though you will usually need business KYC first. On DialNexa, that means registration and tax proof, usually reviewed within one business day. Your workspace also needs a compliance ID. Alternatively, if you already have a telecom provider, you can connect it through SIP and keep using your existing numbers. ### **5. Can Voice AI APIs Connect Through SIP?** Yes. With SIP trunking, sometimes called bring your own carrier, you link your existing carrier to the AI platform. On DialNexa, you can authenticate with a username and password or by IP address. Afterwards, run a proper test call, because the built-in check only confirms that the trunk rings. ### **6. Which APIs Support Real-Time Inbound and Outbound Conversations?** You need an API that answers calls on a number and places calls on request. Speech should also stream in real time. That is the baseline for the best voice AI API for outbound and inbound calling. DialNexa, for instance, handles both through the same agent, so one agent can take enquiries and make follow-ups.