CallBridge uses Twilio to make phone calls more accessible for Singapore’s d/Deaf community

Challenge

Deaf people and those with hearing loss in Singapore often need assistance to make phone calls. This limits their ability to manage daily tasks independently.

Solution

CallBridge uses Twilio Programmable Voice to connect calls with speech-to-text and text-to-speech capabilities, enabling users to read what the other caller says and respond by typing. 

Calling the police during an emergency, a bank to update an address or a clinic to change an appointment are tasks that people often take for granted. But to make a simple phone call in Singapore, d/Deaf individuals—who include culturally Deaf people and those with medical hearing loss—often need to find someone to speak for them or take time off work to attend to errands in person.

Mobile app CallBridge gives them a way to make phone calls independently. Using the app, d/Deaf people can type messages that are converted into speech during the call and see the other caller’s voice response on the screen as text.

The app, powered by Twilio Programmable Voice, has already enabled hundreds of d/Deaf users to make phone calls independently.

In 2025, Wayne Tan and Randall Koh were computer science students at the National University of Singapore. As part of a five-person team, they started building CallBridge during a month-long Community Hackathon co-organized by the People’s Association and Open Government Products.

Before deciding what to build, the team spent two weeks speaking to potential users and learning about problems they faced with phone calls. A visit to Deaf Hangouts, a social gathering for members of Singapore’s d/Deaf community, gave them first-hand insights into the difficulty of making important calls.

The team heard that d/Deaf people struggled to contact emergency services. Others had to take time off work to visit banks and other organizations in person because they could not communicate with them by text.

“We spoke to someone at a Deaf Hangouts meetup who mentioned that his father collapsed—he tried to message 995, but it was challenging for him as someone who is hard of hearing,” says Tan. “The story inspired us to build something that works and that d/Deaf and hard-of-hearing users can use 24 hours a day.”

The team initially tried using AI to translate sign language into text. But they found it difficult to interpret facial expressions and other visual cues that can affect the meaning of what someone is communicating.

They decided to focus on phone calls and built CallBridge. The app lets users take part in a phone conversation by converting what the other person says into readable text and allowing users to type a response that the app converts to speech.

During user testing, the team discovered that people on the other end of the call could become confused by the silence while a user was typing. They would not know if the person was still responding or had ended the call.

The team added typing sounds to the call so recipients knew the other person was still typing and had not hung up.

They also introduced a message status system based on the single and double ticks familiar to users of messaging apps. A single tick shows when a message has been sent, and a double tick appears once its audio has finished playing.

“We realized that this is actually really important to our users because, let’s say they send a message, they wouldn’t know when the message has finished playing,” explains Tan.

Users can select male or female voices and choose quick replies for common responses. To smooth out interactions, the app adds a customizable introductory message to let the person answering know that the caller is using a speech app.

After deciding what problem to solve, the team had only about two weeks to create the first working version of their app. They needed a voice infrastructure that could be implemented quickly. The team chose Twilio after considering several options.

“Twilio was one of the most renowned and reputable products that were out there,” says Koh. “Since we had only one month or less than that, we didn’t want to risk relying on unstable infrastructure, and Twilio was a service that we could really put our trust in.”

CallBridge uses Twilio Programmable Voice to connect phone calls to the app’s speech-to-text and text-to-speech services. Twilio Messaging API handles the one-time passwords needed when users register.

Twilio’s regional infrastructure has also helped CallBridge keep its latency low.

“Once a user sends a message, it will be almost immediately played on the call,” says Tan. “It offers lower round-trip latency so the conversation is able to flow naturally.”

Since its launch, CallBridge has helped d/Deaf people in Singapore manage everyday tasks independently. Users have called banks to resolve credit card issues, including getting late fees waived, contacted clinics and hospitals to book medical appointments, and reported maintenance faults to government agencies. Others have used the app to make business enquiries, arrange catering services or contact friends and family.

Koh recalls how one user called their daughter right after being introduced to the app. “The user was deaf and could never make a call to their daughter,” he says. “But CallBridge made that first call possible, and they said it was a really meaningful experience.”

Another user welcomed the convenience of arranging a medical appointment without assistance: “I am loving this, as it is much more convenient for me to call the clinic for my flu vaccine appointment.”

In less than a year, the app has enabled more than 2,250 completed outbound calls, with over 200 users successfully making calls independently. It has also achieved an average satisfaction rating of 4.1 out of 5 across 135 in-app reviews.

CallBridge’s next priority is to reach more d/Deaf and hard-of-hearing people in Singapore.

“We want more people to know about CallBridge and feel comfortable receiving these calls,” says Koh. “If more people understand how it works, it will be easier for our users to make calls.”

Partnering with key organizations is a priority to make sure users get the support needed to make successful calls. The team is looking to run corporate social responsibility workshops for organizations to teach their team members more about the d/Deaf and hard-of-hearing community. These workshops could generate revenue for CallBridge and help more users make calls.

The team will continue to use Twilio as the voice infrastructure for CallBridge as it reaches more users and gathers feedback from them.