How Rehearsals increased call completion rates from 35% to 90% with Phonic

The Challenge

An awkward voice experience was holding back call completion rates

Rehearsals is an consumer research platform for marketing teams that predicts marketing outcomes by simulating opinions of real people. To build each twin, they run multiple hours of voice interviews with real humans to understand the emotions that drive their purchase.

If the interview is more engaging, the user tends to share more and more information, which leads to a more comprehensive dataset for a digital twin. Conversely, if the AI interview is awkward and uninviting, then the user is brief and terse in their replies.

Liam (Co-Founder, CEO) knew that a better voice experience would help unlock substantially better research reports for his customer, but building it proved elusive. “Our team spent countless hours switching between GPT Realtime, Gemini Live, and others to try and find the models that sucked the least”, he said, “We would spend hours trying to fix mispronunciations, missed tool calls, and playing around with the thinking budget while trying to maintain low latency.”

"I would probably see that at least one out of four times where it pronounces something really weird. I would go talk to the Gemini team and they would say ‘Cool. We can’t do anything about it.’.”

Liam Bolling
CEO of Rehearsals

The Solution

A true voice partner, not a Frankenstein’d stack

After seeing a demo of Phonic, Liam immediately felt like the voice naturalness, latency, and polyglot ability was a step change from what he had seen before. Within hours of the partnership’s start, a coding agent had migrated their implementation to Phonic and Rehearsals was live running calls.

The magic showed up almost immediately: while the previous stack would constantly interrupt users mid-answer, Phonic listened patiently as they considered their response. While the previous stack listened quietly to users speaking lengthy answers, Phonic nodded along with backchannels ("mmhmmm"), signaling that it was following along.

A small A/B test showed value within hours: call durations increased, users started answering the questions with more depth and nuance, and the value of having a more engaging voice went from a promise to a reality. "All of a sudden, the question changed from: do we adopt Phonic, to how can we adopt this as quickly as possible", said Liam.

The answer, it turned out, was to not even think about it. “Phonic made the transition a breeze”, said Liam, “The team went as far as to listen to every call once we were live and provided suggestions on how to update our supervisor agent to have a more natural experience. I felt like Phonic had my back to make the transition easier for me.”

The support didn’t stop once Rehearsals was live. When Brian, an engineer on the team, was looking to build push-to-talk support, he first tried to build it himself before asking Phonic if it could be supported. When Phonic shipped it by the end of the day, Brian texted Liam “these guys are nuts”.

While the voice quality increased and latency decreased, the biggest payoff by far was in the polyglot ability. Rehearsals' customers are multinational conglomerates: they aren't just interested in what people in English-speaking countries think, but also regions like Italy, Spain, and Japan. Before Phonic, a new language requirement meant re-evaluating voices, tuning latency, and understanding new failure cases. Since all of Phonic's voices are tuned across 50+ languages, so adding a new language was as simple as clicking a button.

"One of the huge unblocks is that we were really easily able to take Phonic and then swap it over to Mandarin, French, Italian — all these different languages. That's what our customers really wanted. And that unlocked Europe and Asia... that was a massive TAM unlock. We're gonna be one of the first — because of your model's capability of speaking any language we throw at it — one of the only panels in the world where we have coverage in every country that people really want to sell to."

Liam Bolling
CEO of Rehearsals

The Outcome

2.5x higher call completion rates and freed up 15% engineering time

After implementing Phonic, Rehearsals saw:

1. Their call completion rate soared from 35% to 90%
2. The number of mispronunciations of key terminology happened from ~25% of calls to virtually 0 calls.
3. They freed up 15% of engineering bandwidth that previously was spent maintaining their voice stack and solving edge cases
4. Rehearsals could address a 4x larger market size because the multilingual abilities were incredibly natural and life-like

"If you care about your customers and you want them to feel like they're speaking to a person that's attentive and understands them and speaks like them and it's a natural experience, then there is quite literally nothing else on the market anywhere near what Phonic has. It's impossible. OpenAI, DeepMind, Anthropic, anything on Hugging Face — there's nothing that comes even within striking distance of what [Phonic] provides."

Liam Bolling
CEO of Rehearsals