# ChatGPT Voice API Mobile App Template, Free for iOS

> By Lawrence Arya, Founder & CEO of VP0. Published 2026-06-01, updated 2026-06-02. 5 min read.
> Source: https://vp0.com/blogs/chatgpt-voice-api-mobile-app-template

A voice app is a state machine you can hear. Listening, thinking, speaking: make each unmistakable, then connect a realtime voice API.

**TL;DR.** A ChatGPT voice style app is a visible state machine over a realtime voice API: a clear listening state with a reactive orb, thinking, speaking, plus an interrupt and an optional transcript. Build the UI free from a VP0 design in SwiftUI, prototype the states with sample audio, then connect a voice or realtime API, capturing mic and playing audio. Route the call through a backend so your key is safe. The state clarity is the product.

Building a ChatGPT voice API mobile app? The short answer: a voice app is a state machine you can hear, listening, thinking, speaking, and the whole job is making each state unmistakable, then connecting a realtime voice API. Build the UI free from a VP0 design, the free iOS design library for AI builders, in SwiftUI, prototype the states, then wire the API through a backend so your key is safe. The state clarity is the product. By the numbers, about 76% of developers [now use or plan to use AI tools](https://survey.stackoverflow.co/2024/ai) in their work.

## Who this is for

This is for builders making a voice assistant or voice-mode AI app for iOS who want responsive, legible voice states without paying for a kit, and who will connect a realtime voice API.

## What a voice app has to get right

Voice is invisible, so the screen carries the feedback. The listening state must be unmistakable, a reactive orb or waveform responding to the mic, so the user knows they are heard. Thinking shows the model is working, not frozen. Speaking shows it is the app's turn, with subtle motion. An interrupt lets the user cut in, which makes it conversational, and an optional transcript lets them verify. Underneath, capture the mic, play the audio, and keep your key off the device. The [Apple Human Interface Guidelines](https://developer.apple.com/design/human-interface-guidelines) cover the layout, [AVAudioEngine](https://developer.apple.com/documentation/avfaudio/avaudioengine) handles audio, and a realtime voice API like the [OpenAI realtime API](https://platform.openai.com/docs) supplies the conversation, called via your backend.

| State | Job | Get it right |
|---|---|---|
| Listening | Show you are heard | Reactive orb or waveform |
| Thinking | Show it is working | Not a frozen screen |
| Speaking | App's turn | Subtle, clear motion |
| Interrupt | Take a turn | One tap, always available |
| Transcript | Verify | Optional, readable |

## Build it free with a VP0 design

Pick a voice screen in VP0, copy its link, and prompt your AI builder:

> Build a SwiftUI voice app from this design: [paste VP0 link]. A central orb reacting to mic input while listening, distinct thinking and speaking states, an interrupt button, and an optional transcript. Capture mic audio and play responses, and call my backend for the voice API. Match the palette and spacing from the reference, and generate clean code.

For neighboring voice and AI patterns, see [an AI voice agent UI screen](/blogs/ai-voice-agent-ui-screen/), [a Google Gemini Live voice assistant UI template](/blogs/google-gemini-live-voice-assistant-ui-template/), [building an AI wrapper app in SwiftUI in 5 minutes](/blogs/build-ai-wrapper-app-swiftui-5-minutes/), and [how to make an AI app look native on iOS](/blogs/make-ai-app-look-native-ios/).

## Build the states before the API

You do not need a live voice API to design the experience. Drive the orb with sample audio levels and script the timing of thinking and speaking, so you can tune each state and transition until a turn feels natural. Then connect a realtime voice API, request mic permission in context, and make the visual state strictly follow the real one, never showing listening when the mic is off. Route the call through a backend or token service so your key stays safe. The transitions are the craft, because a voice app that leaves the user unsure whose turn it is feels broken no matter how good the model.

## Common mistakes

The first mistake is states that look too similar, so the user cannot tell listening from thinking. The second is a frozen thinking state. The third is no interrupt, which kills the conversational feel. The fourth is shipping the API key in the app. The fifth is asking for mic permission before the user understands why.

## Key takeaways

- A voice app is a state machine you can hear; make each state unmistakable.
- Make listening reactive, and add a clear interrupt for a conversational feel.
- VP0 gives you the voice UI free, ready to build with Claude Code or Cursor.
- Prototype the states with sample audio, then connect a realtime voice API.
- Route the API through a backend so your key is never in the app.

## Frequently asked questions

How do I build a ChatGPT voice style app for iOS? Build a visible state machine, listening, thinking, speaking, plus interrupt and transcript, then connect a realtime voice API, with the UI from a free VP0 design and the call routed through a backend.

What is the best free voice app template for iOS? VP0, the free iOS design library for AI builders, which generates clean SwiftUI for the orb and states from a design link.

What states does a voice app need? Idle, listening, thinking, speaking, and error. The user must always know whose turn it is, with an interrupt for a conversational feel.

How do I keep the API key safe in a voice app? Route the voice API through a backend or token service rather than embedding the key in the app.

## Frequently asked questions

### How do I build a ChatGPT voice style app for iOS?

Build a visible state machine, listening with a reactive orb, thinking, speaking, plus an interrupt and optional transcript, then connect a realtime voice API, capturing mic input and playing audio. Build the UI in SwiftUI from a free VP0 design, prototype with sample audio, and route the API through a backend so your key is safe.

### What is the best free voice app template for iOS?

VP0, the free iOS design library for AI builders. You clone a voice screen into an AI tool like Claude Code or Cursor, which generates clean SwiftUI for the orb and states, at no cost, then you connect a voice API.

### What states does a voice app need?

Idle, listening, thinking, and speaking, plus error. The user must always know whose turn it is and that they are heard, so each state needs a distinct, unmistakable visual, and an interrupt makes it feel conversational.

### How do I keep the API key safe in a voice app?

Route the realtime or voice API call through a backend or token service rather than embedding the key in the app, so it cannot be extracted, and you can manage usage and limits.

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*Published on the [VP0 Journal](https://vp0.com/blogs). Free to read, index and cite with attribution.*