Twilio

Three strengths

• Calls inside your app. Its Voice SDKs add internet calling directly to web and native mobile apps. 2
• Calls that get through. Its Network Traversal Service helps the SDKs connect across restrictive networks. 3
• Multiple tools in one. It also handles text messaging, video calls inside an app, email through SendGrid and a contact centre product. 5

What it is

A call made from inside an app runs over the internet, not the phone network. This is called VoIP, short for voice over IP. Twilio is a platform that provides it to developers. It was founded in 2008 to simplify the complexity of the global telecommunications network. 1 Its Voice SDKs "allow you to add voice-over-IP (VoIP) calling directly into your web and native mobile applications", with kits for JavaScript in the browser and for iOS, Android and React Native. 2

Making internet calls dependable is harder than it sounds. Most devices sit behind a router that uses NAT (network address translation), and the internet engineering standard for relaying notes that a device behind NAT can find it impossible to communicate directly with another device. The fix is an intermediate node that acts as a relay. 4

Twilio's Network Traversal Service provides that: a global service for the standard techniques known as STUN and TURN, which improves connections for apps that use WebRTC (a browser technology for live audio and video) and VoIP. The SDKs can use them to traverse restrictive networks, and the service routes calls to the nearest geographic server. 3

Twilio's platform covers more than voice. It also handles text messaging across SMS, WhatsApp and other channels, video calls inside an app, email through SendGrid, and a contact centre product called Flex that routes customer conversations to the right agent. 5

We choose it because internet calling is a hard problem that Twilio already has kits for, and those kits fit the web and mobile apps we build.

How we use it

If your app needs people to talk to each other, calling can be built right into it. We've used Twilio for exactly that, through its Network Traversal Service, in a mobile app with a calling feature. We haven't used it for text messages, opting instead to support direct messaging in our apps with WebSockets.

That's Software Development at work: building the features your customers use into an app designed around them. For you, it means calling becomes part of an app tailored to your product, which is the tailored solutions and human-centred design the service is built around.

References

1. Twilio, "About Twilio", twilio.com. https://www.twilio.com/en-us/company (accessed 29 October 2026)
2. Twilio, "Voice SDKs", Twilio Docs. https://www.twilio.com/docs/voice/sdks (accessed 29 October 2026)
3. Twilio, "Network Traversal Service", Twilio Docs. https://www.twilio.com/docs/stun-turn (accessed 29 October 2026)
4. T. Reddy, A. Johnston, P. Matthews and J. Rosenberg, "Traversal Using Relays around NAT (TURN): Relay Extensions to Session Traversal Utilities for NAT (STUN)", RFC 8656, IETF, 2020. https://www.rfc-editor.org/rfc/rfc8656 (accessed 29 October 2026)
5. Twilio, "Twilio Docs", twilio.com. https://www.twilio.com/docs (accessed 29 October 2026)