Voice agent platforms look similar in a demo. Each one lets you write a prompt, pick a voice, and talk to your agent in a browser. The differences show up later, on real phone lines, with real callers who interrupt, mumble and ask things you did not plan for.
This guide does not rank providers. Features and prices change often, and any ranking we wrote would age quickly. Instead, it gives you the criteria to compare and a way to test them yourself. For every item below, confirm current details in each vendor’s own documentation.
#What to evaluate
Put these on your scoring sheet:
- Response delay on real phone lines. The pause between the caller finishing a sentence and the agent starting to speak. Test on a phone, not in the browser.
- Interruptions and turn-taking. What happens when the caller talks over the agent, says “uh-huh,” or pauses mid-thought?
- Voice quality in English and Spanish. Names, numbers, addresses and accents. If you serve both languages, test both, including a caller who switches mid-call.
- Phone numbers and carrier setup. Can you buy numbers, bring your own, or connect an existing line? How long does setup take, and what restrictions apply in your country?
- Transcripts and recordings. Where they are stored, how fast they appear, and how you can export them. Test an actual export.
- Hand-off to a human. Can the agent transfer the call, to which numbers, and what does the person receive (a summary, the transcript, nothing)?
- Tool and webhook calling. Can the agent call your own systems during the call to check a booking or look up an order? Check timeouts and what happens when your system is slow.
- Pricing structure. Not just the per-minute rate, but what is billed separately: telephony, the language model, the voice, transcription, extra concurrent calls, recordings storage.
- Reliability and status history. Read the public status page and past incident notes. Ask what happens to calls in progress during an outage.
- Data retention and privacy. How long data is kept, where, who can access it, and whether you can delete it. This matters most if callers share personal or health details.
#Run a bake-off
A bake-off means giving every provider the same test and scoring the results the same way.
- Write one script and one set of instructions for the agent, and use them on every platform. Keep the prompt the same, even if one platform handles it a little better with changes.
- Write 10 test calls. Include easy ones (a plain booking), awkward ones (a caller who interrupts, a noisy line), a Spanish call, a call that needs a hand-off to a person, and a call that needs a lookup in one of your systems.
- Use the same phone line or handset for every call, and the same caller for each scenario so differences come from the platform, not the person.
- Score each call right after it ends, before you hear the next platform.
- Review the transcripts and recordings afterward. Check whether the transcript matches what was actually said.
#The scoring sheet
Make one row per criterion and one column per provider. Score each from 1 to 5 and add a note on why. Weight the rows that matter for your business. A clinic may weight privacy highest; a restaurant may care most about response delay and Spanish.
Do not average the totals blindly. If a provider fails a must-have (say, it cannot transfer calls to your number), it is out regardless of its other scores.
#Plan for switching
Your choice does not have to be permanent. Keep prompts, scripts and knowledge content in your own documents, not only inside a vendor’s dashboard. Export transcripts regularly. Ask how you would move numbers to another provider.
Altamar’s Teldash portal is an example of why this matters: it works with agents built on ElevenLabs, Retell or Vapi, so the voice platform and the tools around it can be separate choices. You can read how it works in the Teldash case study.
#Confirm before you commit
After the bake-off, read each vendor’s current documentation and pricing page for the items that decided your scores. Then run a small paid pilot on live calls before you move everything over.
