Vapi, Retell and Synthflow alternatives for agencies (2026)
If you're an agency reselling AI voice agents, the best alternatives to Vapi, Retell AI and Synthflow are whitelabel platforms that include client dashboards and rebilling out of the box: Outbox AI, Trillet, Autocalls and Stammer AI. If you want to keep your existing Vapi or Retell agents, add a whitelabel layer like VoiceAIWrapper instead.
Disclosure: we make Outbox AI. Every competitor fact below comes from that company's own pricing page or docs, checked on 3 October 2026.
Why agencies look for alternatives
Vapi, Retell AI and Synthflow are all good at running voice agents. The problem for an agency is everything around the agent.
- Vapi and Retell are developer platforms. Neither ships a whitelabel client portal or client rebilling. Both list third-party partners that add them (Vapify, VoiceAIWrapper, ChatDash and others). To sell to clients under your brand you add another vendor or build your own dashboard, billing and sub-accounts.
- Their per-minute price isn't the whole price.
- Vapi: $0.05/min for hosting. Transcription, model, voice and telephony are billed on top.
- Retell: $0.055/min for voice infrastructure, plus model, voice and $0.015/min telephony. Retell estimates $0.07-$0.31 a minute all-in.
- That's fine for one in-house build, but hard to quote to fifty clients.
- Synthflow changed course. Synthflow's public pricing is now enterprise-only, starting at $30,000 a year. Its docs say the Stripe integration for reselling to sub-accounts was removed on 15 September 2026, so agencies that relied on it now bill clients themselves.
Two ways to replace them
Route 1: switch to an all-in-one whitelabel platform
The platform runs the calls and gives you the branded client dashboard, sub-accounts and billing. One vendor, one bill, and a single per-minute price you can mark up.
| Platform | Monthly from | Custom-domain whitelabel | Client rebilling | AI voice per minute |
|---|---|---|---|---|
| Outbox AI | $97 | From $97 (Starter) | Stripe, from $149 (Growth) | 14¢ / 12¢ / 10¢, model and voice included |
| Trillet | $99 (1,000 min incl.) | $299 (Agency) | Stripe | $0.12 after included minutes, telephony extra |
| Stammer AI | $49 ($99 for whitelabel) | $99 | Yes | $0.11-$0.17 by model |
| Autocalls | $34 ($419 for whitelabel) | $419 monthly / $355 annual | Stripe | $0.09 overage on top tiers |
| Bland AI | $0 (Start) | Not offered publicly | No | $0.14 (Start), $0.12 on the $299 Build plan |
Route 2: keep Vapi or Retell and add a whitelabel layer
If you've already invested in Vapi or Retell agents, a wrapper gives you the client-facing layer without migrating. VoiceAIWrapper ($79-$499/month) sits on top of Vapi, Retell, ElevenLabs, Bolna or Ultravox using your own keys. It adds a custom domain, client accounts and Stripe rebilling, with no per-minute markup.
The trade-off: you still pay your provider's separate model, voice and phone charges, you manage two vendors, and CRM integrations like GoHighLevel run through webhooks.
Outbox AI as a Vapi, Retell or Synthflow alternative
Outbox AI is built for the agency use case these tools leave to you.
- Whitelabel from day one: your logo, custom domain and sender email on the $97 Starter plan.
- Rebilling built in: connect your Stripe account, set your own per-minute and per-message rates, and client wallets top up automatically (Growth and up). There's no revenue share, and you can publish self-serve SaaS plans for clients.
- One predictable rate: 14¢, 12¢ or 10¢ a minute depending on plan, with model usage included, so you can quote clients a margin without a spreadsheet.
- Production voice: sub-800ms responses, barge-in, and warm transfers with a summary or a concierge-style handover. Runs on Twilio, Vonage, Telnyx or SIP.
- More than voice: chat agents on SMS, WhatsApp, Messenger, Instagram and web, plus workflows and AI-built client websites, under the same brand.
- Native GoHighLevel: a marketplace app with Send AI Call and AI chat workflow actions (details).
Where Vapi or Retell is still the better pick: if you're a developer building one highly custom agent and want low-level control over every model, voice and telephony component, the raw APIs give you more knobs. Outbox trades some of that low-level control for a platform you can sell from on day one.
Migrating from Synthflow, Vapi or Retell
- Export your prompts. Your system prompt, first message and knowledge base text carry over almost as-is.
- List your tools. Map each function or webhook to the new platform's equivalent. On Outbox that's a built-in tool (book appointment, SMS, transfer, CRM update), a custom webhook, or an MCP server.
- Move or forward your numbers. Bring your Twilio, Telnyx or Vonage numbers, or point your SIP trunk at the new platform.
- Run both side by side on a test number for a few days, using the same scripts, and compare responses, booking accuracy and cost per call.
- Switch the client over, then turn on rebilling.
Frequently asked questions
What is the best Vapi alternative for agencies?
For agencies that resell to clients, an all-in-one whitelabel platform such as Outbox AI, Trillet or Autocalls is usually better than Vapi, because it includes branded client dashboards, sub-accounts and rebilling. Vapi is a developer API without those agency features.
What is the best Synthflow alternative after the 2026 pricing change?
Agencies that relied on Synthflow's sub-account reselling, which was removed on 15 September 2026, should look at platforms with built-in Stripe rebilling. Outbox AI (from $149/month), Trillet (from $99/month) and Autocalls (from $355/month annual) all include it.
Is Retell AI white-label?
Not natively. Retell has no whitelabel client portal or client rebilling of its own, but lists third-party partners that add them. Alternatively, use a platform like Outbox AI that includes whitelabel and rebilling.
How much does Vapi really cost per minute?
Vapi charges $0.05 a minute for hosting, plus transcription, the language model, the voice and telephony, each billed at the provider's rate. Retell estimates $0.07-$0.31 a minute all-in for its own platform. Outbox AI charges 10-14¢ a minute with model and voice included; carrier minutes are billed by your carrier.
Can I keep my Vapi agents and still whitelabel them?
Yes. Tools like VoiceAIWrapper add a whitelabel client portal and Stripe rebilling on top of your existing Vapi or Retell account.
Sources
Checked on official sites on 3 October 2026: Vapi pricing, Vapi whitelabel partners, Retell AI pricing, Retell app partners, Synthflow pricing, Synthflow Stripe reselling notice, Trillet whitelabel pricing, Stammer AI pricing, Autocalls pricing, Bland AI pricing, VoiceAIWrapper pricing.