Voice AI agents that answer and place calls on Rexenda phone numbers, answer WhatsApp calls and call contacts on WhatsApp who have agreed to be called. They speak natural Spanish and English, switch to the caller's language and let callers interrupt.
A Synthflow alternative with AI voice agents, WhatsApp and a free plan forever
Synthflow is a voice AI platform for automating phone calls, with a visual no-code builder, its own telephony and sales-led enterprise contracts. Rexenda is a self-serve business application where AI agents answer and place phone and WhatsApp calls, reply on WhatsApp and other chat channels, and work inside a built-in CRM, calendar and quotes.
- Free plan, no time limit
- No credit card required
Why teams look for a Synthflow alternative
Contract size. According to Synthflow's pricing page, enterprise contracts start at $30,000 a year, scoped around call volume, concurrency, telephony, integrations and launch support, and the page does not list a self-serve plan.
A sales-led start. Getting started goes through a demo or the sales team, with implementation, onboarding and launch support scoped in the contract, which fits large rollouts more than a small team that wants to try on its own today.
WhatsApp limits. Synthflow's documentation says WhatsApp Business Calling works with inbound agents only, and that WhatsApp messaging runs through your own Twilio account and is available for US-region workspaces.
What Rexenda does differently
WhatsApp messaging connects directly through Meta's Embedded Signup, with no Twilio account in between, and Meta bills message fees to your own WhatsApp Business Account. Instagram, Messenger, web chat, email, SMS and calls share one inbox.
The agent can follow a call with a quote that has an acceptance link, a card payment link paid into your own Stripe account and, for Mexican businesses, a CFDI e-invoice, all from the contact's conversation.
Agents take around 60 real actions in calls and chats: they check availability, book meetings in a calendar synced with Google and Outlook, save the caller's details and move leads through the pipeline. You set them up yourself, without code or an implementation project.
How to switch
Write down how your Synthflow agents greet, qualify and hand off calls, then recreate them in Rexenda from a template or by describing the job. Get a number in the app or request a port of your current one where the carrier allows it, connect WhatsApp with Meta's Embedded Signup and import contacts from a CSV file. If your WhatsApp number is linked to another platform, disconnect it there first, since a number can be linked to only one platform at a time. Make a test call and go live.
When Synthflow may still be the right choice
Synthflow may be the better choice for a large contact center that needs hands-on implementation, an SLA written into the contract, connections to contact-center stacks such as Genesys, Avaya or RingCentral, its own carrier or SIP trunks, and concurrency planned around very high call volumes. Rexenda is self-serve and has no public API with keys today, only outgoing webhooks.
Questions
How is Rexenda different from Synthflow?
Synthflow sells enterprise voice AI rollouts through sales-led contracts with implementation support. Rexenda is a self-serve application with a free plan forever, where AI agents handle phone calls, WhatsApp calls and chats and work inside a built-in CRM with calendar, quotes and payment links. You set up agents without code and pay voice minutes with AI credits.
Do I need an annual contract to use Rexenda?
No. You can start on the free plan forever with no credit card, and paid plans can be billed monthly or yearly. Voice minutes come out of your plan's AI credits, at 12 credits per minute of AI voice call, and phone numbers have a separate monthly charge.
Can Rexenda's voice agent talk to Spanish-speaking callers?
Yes. Rexenda's voice agents speak natural Spanish and English, and with language detection they switch to the caller's language during the call, which suits US businesses that serve customers in both languages. Callers can interrupt at any moment, and the agent responds to what they just said.
Facts about Synthflow checked against its public website in October 2026.
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