Quick answer
Three platforms dominate AI phone agents. Vapi is API-first: pick your own speech-to-text, language model, and voice, with maximum control and a platform fee from about $0.05 a minute plus provider costs. Retell AI bundles telephony and models behind a visual flow builder for around $0.07 a minute. Bland AI runs its own stack for enterprise call volumes from about $0.09 a minute. Engineers pick Vapi, operations teams pick Retell, call centres pick Bland.
A voice agent is three models racing the clock: hear, think, speak, in under a second, while handling interruptions and calling tools mid-sentence. The platforms exist because getting that right is hard, and they differ mainly in how much of the stack they let you touch.
Vapi — the flexible one
- Choose any provider for each layer: Deepgram or AssemblyAI to hear, GPT or Claude to think, ElevenLabs or Cartesia to speak
- Fine control over latency, interruption handling, and function calls
- Per-minute platform fee plus whatever your chosen providers charge — flexible, but four bills
- Requires real engineering
Retell — the fast one
- Visual conversation-flow builder or a single prompt to define the agent
- Telephony, numbers, and models bundled into one per-minute price
- Batch outbound campaigns, post-call analysis, warm transfer to humans
- Less provider choice; complex flows get unwieldy on a canvas
Bland — the enterprise one
- Self-hosted speech and inference for consistently low latency at high volume
- Conversational Pathways for long, branching calls
- Thousands of concurrent calls; sales-led onboarding
- Pricier per minute and overkill for small experiments
What to check before you deploy any of them
- Disclosure and consent laws in every region you call — several now require telling callers they are speaking to an AI
- Hand-off design: the fastest way to lose a customer is an agent that cannot reach a human
- Latency under load, not in the demo
- What happens with accents, background noise, and people who talk over the agent
Related reading
Bottom line
Vapi if you have engineers and opinions about providers. Retell if you want a working agent by Friday. Bland if you are replacing a call centre. All three produce agents callers increasingly cannot tell from people, which is exactly why the disclosure rules matter.
