Provider Comparison
BuildVoiceAI supports three voice AI providers: Retell, Vapi, and Bland. Each provider has distinct strengths, and you can use different providers for different agents. This page helps you choose the right one for your needs.
Feature Comparison
| Feature | Retell | Vapi | Bland |
|---|---|---|---|
| Voice Quality | Excellent | Excellent | Good |
| Latency | Low (~500ms) | Low (~600ms) | Medium (~800ms) |
| Languages | 20+ | 30+ | 10+ |
| Custom Voices | Yes (voice cloning) | Yes (voice cloning) | Limited |
| Knowledge Base | Yes | Yes | Yes |
| Phone Number Support | US, CA, UK + more | US, CA, UK + more | US, CA |
| Function Calling | Yes | Yes | Yes |
| Inbound Calls | Yes | Yes | Yes |
| Outbound Calls | Yes | Yes | Yes |
| Call Transfer | Yes | Yes | Yes |
| Voicemail Detection | Yes | Yes | Yes |
| WebRTC (Browser Calls) | Yes | Yes | No |
| Conversation Interruption | Natural | Natural | Basic |
Voice Quality and Latency
Retell
Retell offers some of the most natural-sounding voices with very low latency. Their proprietary voice engine handles interruptions smoothly, making conversations feel human. Best for high-touch use cases like sales and customer service.
Vapi
Vapi provides excellent voice quality with the broadest language support. Their platform offers the most flexibility in voice customization and supports the widest range of LLM backends. Best for multilingual deployments and advanced configurations.
Bland
Bland focuses on simplicity and high-volume outbound calling. While voice quality is slightly behind Retell and Vapi, it offers competitive pricing for bulk calls. Best for appointment reminders, surveys, and notification-style calls.
Language Support
| Provider | Notable Languages |
|---|---|
| Retell | English, Spanish, French, German, Portuguese, Japanese, Korean, Chinese, and more |
| Vapi | 30+ languages including all major world languages, Hindi, Arabic, Thai, Vietnamese |
| Bland | English, Spanish, French, German, Portuguese |
If you need multilingual agents, Vapi offers the widest language coverage. For English-primary use cases, all three providers deliver excellent results.
Knowledge Base Support
All three providers support knowledge bases, allowing agents to reference uploaded documents during calls. The implementation varies:
- Retell — Upload PDFs and text files directly. Supports URL-based knowledge bases.
- Vapi — Upload documents or connect external knowledge bases. Supports chunking configuration.
- Bland — Upload text-based documents. More limited format support.
Phone Number Management
| Feature | Retell | Vapi | Bland |
|---|---|---|---|
| Purchase numbers in-platform | Yes | Yes | Yes |
| Port existing numbers | Yes | Yes | Yes |
| Toll-free numbers | Yes | Yes | Yes |
| International numbers | Many countries | Many countries | US, CA only |
| Number management in BuildVoiceAI | Full | Full | Full |
Phone numbers are purchased and billed through the provider, not through BuildVoiceAI. Your provider account must have billing set up to purchase numbers.
Pricing Model
Each provider has its own pricing structure. BuildVoiceAI does not add a markup on provider costs — you pay the provider directly based on your usage.
| Provider | Pricing Basis |
|---|---|
| Retell | Per-minute based on voice model and features used |
| Vapi | Per-minute with separate rates for telephony, voice, and LLM |
| Bland | Per-minute flat rate, volume discounts available |
Provider pricing changes independently of BuildVoiceAI. Always check the provider’s current pricing page for the latest rates.
Recommendations by Use Case
Sales and Lead Qualification
Recommended: Retell or Vapi
Low latency and natural interruption handling are critical for sales conversations. Both providers excel at natural-sounding dialogue.
Appointment Reminders and Notifications
Recommended: Bland
For high-volume, short calls where the script is straightforward, Bland offers competitive pricing and reliable delivery.
Multilingual Support
Recommended: Vapi
With 30+ languages, Vapi is the clear choice for agencies serving a global market or multilingual customer bases.
Customer Service and Support
Recommended: Retell or Vapi
Both providers handle complex conversations well with strong function calling support for looking up account information and performing actions.
Surveys and Feedback Collection
Recommended: Bland or Retell
Structured conversations like surveys work well on all providers. Choose based on volume and budget.
Using Multiple Providers
BuildVoiceAI is provider-agnostic. You can:
- Use different providers for different agents
- Connect multiple provider accounts simultaneously
- Switch an agent’s provider by creating a new agent on the desired provider
Each provider requires its own API key configured in Settings → Integrations. You only need to set up the providers you plan to use.
Provider Status Pages
Monitor provider uptime and incidents: