Twilio and Sony Partner to Enable Voice Calling on Low-Power, LTE-M Cellular IoT Devices

June 15, 2022
Written by
Dana Cohen Mizrahi
Opinions expressed by Twilio contributors are their own
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Embedded Voice over LTE-M

Voice is still the preferred choice for people who want to communicate, and millions of developers already know how Twilio gives them the power to add voice communications to their products with just a few lines of code. These products, such as wearables, IoT, and smart devices are getting smaller and smaller and becoming more a part of our lives every day. Now with Sony Semiconductor and Twilio, you can quickly and easily add voice communications to your small-footprint, low-power, and low bandwidth IoT device. All you need is an ALT1250 chipset within your device, a SIP or WebRTC client and a microphone and speaker. This new capability means simplified design and reduced cost for portable, low-power IoT devices with global voice functionality.

Sony ALT1250

Designed for cellular IoT applications from the ground up, the Sony ALT1250 drives devices which prioritize battery life, security, and small size, ensuring compliant and reliable network connectivity. This full-solution, 5G-ready, Dual-Mode LTE-M & NB-IoT chipset with 2G fallback is built to evolve along with the IoT service and cellular network. Ultra-low power, small size, security and high level of integration make the ALT1250 attractive for designers of alarm panels, access control systems, trackers, child & adult wearables, fitness & patient monitoring devices, smart metering and many other IoT applications.

Twilio Programmable Voice, SIP, the AMR-NB Codec, and Super SIM

Twilio’s SIP Interface functionality allows you to augment your VoIP Infrastructure using cloud-based capabilities. Customers use it to build out their communications and voice applications, then change, improve, and scale the deployment across different office sites and numbers. Multi-site installations, BYOC (bring your own carrier), and more are all possible using industry-standard SIP solutions.

Now, Twilio has added a key feature that will enable low-power, cellular network voice communications. With the addition of support for the AMR-NB codec (in Limited Availability, contact us to try it out), it is now feasible to use SIP solutions over Sony ALT1250-based cellular LTE-M devices, without the need for Voice over LTE (VoLTE). AMR-NB allows for a low-bandwidth media stream, which is effective for use with ALT1250 low-power devices on cellular networks.

To complete the picture, Twilio Super SIM can give you access to LTE-M networks that provide the low-power features required for battery-operated device longevity.

Mixing it all together for a functional setup

Twilio and Sony set out to test the viability of integration voice communications on a device built using the ALT1250 chipset over an LTE-M commercial network, connecting through Twilio Super SIM.

How a Sony ALT1250-based device connects to the PSTN through the Twilio Cloud
How a Sony ALT1250-based device connects to the PSTN through the Twilio Cloud

We had two basic SIP clients, registered to Twilio using the Programmable Voice SIP interface:

  1. SIP Client A: Sony proprietary interface, running on Sony’s ALT1250 demo board
  2. SIP Client B: Open-source MicroSIP client, running on a PC

On the Twilio side, we set up a Programmable Voice SIP Domain (for the purposes of this blog let’s call it ‘’), and registered both SIP clients to that domain using the SIP Registration functionality. Then, just the simplest of applications; TwiML that bridges an inbound call from Client A to Client B using the <Dial> verb and <Sip> noun:

<?xml version="1.0" encoding="UTF-8"?>

Then, we enabled the new AMR-NB codec on the Twilio account we were using for testing, and had the client on the ALT1250 device (Client A) set that codec as its primary codec. As mentioned above, that change allows a low-bandwidth media stream, which is the key functionality for this LTE-M network solution.

Admittedly, this was a very simple test scenario, but it worked very well. Calls completed, and both parties were easily able to communicate with each other. The low-bandwidth codec performed well on the LTE-M network, and we saw minimal packet loss and jitter over the course of the calls. Obviously, performance can vary with network quality and availability, but in areas with consistent cellular network signals, the expectations would be clear audio communications.

To understand the resulting call flow better, please have a look at this short video demonstration. In our video, we assume a mobile phone on the other end vs. a PC.


With this simple connection to build from, you open up a myriad of possibilities and scenarios of how you can digitally transform and power up your voice communications using Twilio and Sony’s ALT1250 based devices. Customize your experience the way you want; build an engaging voice experience that you can quickly scale and modify with a wide array of customization options and resources. Add on features like Interactive Voice Response (IVR), recording transcriptions, and speech recognition to create an experience that you and your customers will appreciate. Build alerts and notifications into your device solutions. Use call tracking to unlock the data embedded in your calls. Or build something nobody has before and only pay for what you use; no long-term contracts or minimums.

How do I get started with Embedded Voice over LTE-M?

For more information about the Sony’s ALT1250 chipset, visit the Sony website, and fill out the Contact form. For ongoing information follow Sony Semicon on LinkedIn or Twitter.

For more information about the Twilio technology and to get access to the AMR-NB codec, visit the Twilio-Sony solution page.

We can’t wait to see what you build!