Best Phone Automation

Synthflow vs Retell AI

Synthflow sells annual enterprise agreements with no public price. Retell AI bills by the minute from the first call.

Updated By the Best Phone Automation deskHow we scoreDisclosure

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Short answer

Retell AI wins for any business that wants to start this week: it scores 7.9 against Synthflow's 6.2, publishes its rates and starts with $10 in free credits23. Synthflow fits contact centers that want agents inside Five9, Zoom or RingCentral and can sign an annual contract91.

Pick Synthflow if
you run an enterprise contact center, BPO or multi-location brand, want agents inside Zoom, Five9 or RingCentral, and need SOC 2 Type 2, ISO 27001 and EU hosting911.
Pick Retell AI if
you want to sign up today, see the price before the first call and pay by the minute with no contract2.
Synthflow and Retell AI compared
SynthflowRetell AI
Our score6.27.9
How it is soldAnnual enterprise agreement after a scoping call1Pay as you go, with no contract or minimum2
Published priceNot published1$0.07 to $0.31 a minute for voice agents2
Free trialNo1$10 in credits, no payment method until you buy a phone number3
Time to go liveWeeks; Batteries Plus took five weeks from kick-off to pilot415 minutes in the quick start3
BookingCal.com or GoHighLevel5Cal.com, Calendly or GoHighLevel6
Transfer to a personCold, warm with a message, or warm with an AI summary7Cold, warm and agentic warm8
Phone systemsBuilt-in connections for Zoom, Five9, RingCentral, 8x8, Twilio, Telnyx, Vonage and Freshcaller9Any system through SIP trunking10
Security and hostingSOC 2 Type 2, ISO/IEC 27001, PCI DSS v4.0.1, HIPAA BAA; US or EU hosting11SOC 2, HIPAA, GDPR, ISO 27001:2022, CCPA12; no services inside the EU13

Scores by criterion

Synthflow

Score breakdown for Synthflow
Call quality 25%8.0
Setup 20%4.0
Integrations 15%8.5
Price 20%2.0
Trust 10%9.0
Support 10%8.0

Retell AI

Score breakdown for Retell AI
Call quality 25%8.5
Setup 20%6.5
Integrations 15%8.5
Price 20%8.0
Trust 10%8.0
Support 10%7.5

Visit Synthflow (opens the Synthflow website)Visit Retell AI (opens the Retell AI website)

Questions people ask

Does Synthflow have a free trial like Retell AI?

No. Synthflow has no free plan or trial and publishes no per-minute rate1. Retell AI starts with $10 in free credits and no payment method3.

Which is better for a contact center, Synthflow or Retell AI?

Synthflow, if the center runs on Five9, Zoom, RingCentral, 8x8 or Twilio: it ships built-in connections for each9 and assigns a Customer Success Manager and a shared Slack channel14. Retell AI connects any phone system through SIP trunking10 and lets a supervisor listen in and take over a live call15.

Sources

  1. Synthflow (AgentFlow AI GmbH). AI Voice Agent Pricing for Enterprise | Synthflow. Checked 9 Nov 2026.
  2. Retell AI. AI Phone Agent Pricing | Retell AI. Checked 9 Nov 2026.
  3. Retell AI documentation. Build your first Retell AI phone agent in 15 minutes. Checked 9 Nov 2026.
  4. Synthflow (customer story). Batteries Plus Runs AI Voice Agents on Zoom Phone | Synthflow. Checked 9 Nov 2026.
  5. Synthflow Docs (docs.synthflow.ai). Real-Time Booking | Synthflow. Checked 9 Nov 2026.
  6. Retell AI documentation. Connect your CRM, calendar, helpdesk, and knowledge sources to Retell AI. Checked 9 Nov 2026.
  7. Synthflow Docs (docs.synthflow.ai). Call Transfers | Synthflow. Checked 9 Nov 2026.
  8. Retell AI documentation. Transfer calls with single and multi-prompt agents. Checked 9 Nov 2026.
  9. Synthflow (AgentFlow AI GmbH). Enterprise AI Voice Agents for Phone Calls | Synthflow. Checked 9 Nov 2026.
  10. Retell AI. AI Voice Agents That Automate Phone Calls | Retell AI. Checked 9 Nov 2026.
  11. Synthflow (AgentFlow AI GmbH). Voice AI Security and Compliance: SOC 2, HIPAA | Synthflow (last reviewed November 5, 2026). Checked 9 Nov 2026.
  12. Retell AI (Vanta-hosted trust center). Retell AI Trust Center. Checked 9 Nov 2026.
  13. Retell AI documentation. Retell AI security and compliance: HIPAA, GDPR, SOC 2, and data erasure. Checked 9 Nov 2026.
  14. Synthflow Docs (docs.synthflow.ai). Getting support | Synthflow. Checked 9 Nov 2026.
  15. Retell AI documentation. Monitor live Retell calls: listen in, take over, or end a call. Checked 9 Nov 2026.