Provider Comparison
BuildVoiceAI supports four voice AI providers: Retell, Vapi, Bland, and ElevenLabs. 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 | ElevenLabs |
|---|---|---|---|---|
| Voice Quality | Excellent | Excellent | Good | Excellent |
| Latency | Low (~500ms) | Low (~600ms) | Medium (~800ms) | Low (Flash v2) |
| Languages | 20+ | 30+ | 10+ | 70+ |
| Custom Voices | Yes (voice cloning) | Yes (voice cloning) | Limited | Yes (5,000+ voices) |
| Knowledge Base | Yes | Yes | Yes | Yes (document upload) |
| Phone Number Support | US, CA, UK + more | US, CA, UK + more | US, CA | Via Twilio SIP trunking |
| Function Calling | Yes | Yes | Yes | Yes |
| Inbound Calls | Yes | Yes | Yes | Yes (via Twilio SIP) |
| Outbound Calls | Yes | Yes | Yes | No |
| Call Transfer | Yes | Yes | Yes | Limited |
| Voicemail Detection | Yes | Yes | Yes | No |
| WebRTC (Browser Calls) | Yes | Yes | No | Yes |
| Conversation Interruption | Natural | Natural | Basic | Natural |
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.
ElevenLabs
ElevenLabs Conversational AI offers the largest voice catalog (5,000+ voices) with the widest language support (70+ languages). Their Flash v2 model delivers low latency, while v3 Conversational provides the highest quality. Supports GPT-4o, Claude 4.5 Sonnet, Gemini 2.5 Flash, and other LLMs. Best for multilingual, inbound, and web-based voice experiences. Note that telephony requires Twilio SIP trunking and outbound calling is not supported.
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 |
| ElevenLabs | 70+ languages including all major world languages, with broad accent and dialect coverage |
If you need multilingual agents, ElevenLabs (70+ languages) and Vapi (30+ languages) offer the widest language coverage. For English-primary use cases, all four providers deliver excellent results.
Knowledge Base Support
All four 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.
- ElevenLabs — Upload documents directly to the knowledge base for agent reference during conversations.
Phone Number Management
| Feature | Retell | Vapi | Bland | ElevenLabs |
|---|---|---|---|---|
| Purchase numbers in-platform | Yes | Yes | Yes | No (use Twilio) |
| Port existing numbers | Yes | Yes | Yes | No (use Twilio) |
| Toll-free numbers | Yes | Yes | Yes | Via Twilio |
| International numbers | Many countries | Many countries | US, CA only | Via Twilio |
| Number management in BuildVoiceAI | Full | Full | Full | Limited |
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 |
| ElevenLabs | Credit-based, ~$0.05-0.08/min depending on plan |
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: ElevenLabs or Vapi
ElevenLabs leads with 70+ languages and 5,000+ voices. Vapi also offers strong multilingual support with 30+ languages. Both are excellent choices 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.
Web-Based Voice Agents (No Phone Number)
Recommended: ElevenLabs or Retell
For browser-based voice experiences using WebRTC, ElevenLabs and Retell both offer strong support. ElevenLabs is especially well-suited for inbound and web-only use cases with its massive voice library and broad language support.
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: