Voice agent platforms
Vapi, Retell, Bland, Synthflow and Kallina: how to choose
They all build agents that speak on the phone. They differ in who they are for: some are tools for developers, others are platforms with a visual editor, others are a service where someone builds the agent for you. The page does not give latency or other people’s prices; it sends you to their sources.
How they describe themselves
Summary of the description on each company’s homepage, checked on 15.09.2026. Their wording, not our assessment.
| Platform | How they present themselves | Who it seems to be built for |
|---|---|---|
| Vapi | A platform for developers who build, test and launch voice agents. | Technical teams that want control via API. |
| Retell AI | Voice agent platform for call centres: building, testing, launching and monitoring. | Call centre operations with steady volume. |
| Bland | AI voice platform for large companies, with models hosted by them and an emphasis on compliance. | Large organisations with security requirements. |
| Synthflow | Full AI voice platform for automating calls in companies, for sales and support. | Companies that want to launch without a development team. |
| Kallina | Voice agent platform built on ElevenLabs, with its own telephony server, CRM and campaign integrations, delivered together with the team that builds the agent. | Companies without a dedicated technical team, that want the agent on their line and the result in the CRM. |
Sources, so you can check for yourselves
Vapi
Retell AI
Bland
Synthflow
The questions that decide the choice
Who builds the agent?
If you have developers who want to write the integrations, an API-oriented platform gives you more freedom. If not, it matters who writes the scenario and fixes it after the first calls.
Which line does it call on?
Ask how your existing number is brought over, through which operator, and who responds when the line goes down. Here the differences are bigger than with voice.
Where does the result end up?
Check the integration with the CRM you already use, not the logo list: what is written, in which field, after each call.
How do you pay?
Some platforms charge separately for voice, the language model and telephony. Compare the total cost per minute of a real call, with all components, from their pricing pages.
Where Kallina is not the right choice
You want everything through code
Kallina does not yet have a documented public API. For a product built around an API, choose a platform for developers.
You want to set it up yourself, today
With us, getting started goes through a demo and an offer. Platforms with direct sign-up are faster for a prototype.
You need an integration we do not have
Our list of integrations is short. If your system is not in it and does not have an API, choose a platform that covers it.
Frequently asked questions
Why don't you compare prices?
Platform prices change often and are made up differently. A figure copied today may be wrong tomorrow, so we send you to their pages.
Does Kallina use the same technology as them?
Kallina uses ElevenLabs for voice. The other platforms have their own choices for voice and model, described in their documentation.
Can I move an agent from another platform to Kallina?
Instructions, the knowledge base and the scenarios can be reused. The integrations and telephony are rebuilt in Kallina.
Have you tested these platforms yourselves?
The table shows what they say about themselves. We do not publish our own measurements of other products.
Compare on your call, not on the table
Bring a real scenario to the demo and hear how a Kallina agent takes it to the end.