The SignalWire RELAY Mobile SDK gives developers a real-time communications toolkit for building voice, video, and messaging directly into mobile applications. Instead of building custom realtime stacks from scratch, developers can integrate RELAY into iOS, Android, or cross-platform apps to enable 1-to-1 voice and video sessions, WebRTC media, SIP bridging, and PSTN connectivity while enjoying persistent, low-latency asynchronous connections. This unlocks richer in-app interactions like integrated CRM calling, mobile enterprise comms, and in-game voice/video chat.
Build Real-Time Mobile Communications with the SignalWire RELAY SDK
Mobile applications increasingly demand rich, real-time communication features — from voice and video calling to in-app messaging. The SignalWire RELAY Mobile SDK gives developers the tools they need to integrate high-performance communication directly into iOS, Android, or cross-platform apps without reinventing the entire telecom stack.
RELAY is a next-generation real-time communications protocol that maintains persistent, asynchronous connections using WebSockets, enabling low-latency, bi-directional interactions. This makes it a compelling choice for modern mobile experiences that go beyond old REST-based patterns.
Learn more about RELAY and all supported SDKs in the SignalWire SDK overview.
What Is the RELAY Mobile SDK?
The RELAY Mobile SDK is a set of software development tools that allows you to embed real-time voice, video, and messaging into mobile applications, backed by SignalWire’s powerful RELAY APIs.
Unlike traditional REST APIs, which operate on one-way HTTP requests, RELAY supports persistent, asynchronous connections that make it easier to build responsive, event-driven experiences. This means smoother interactions, real-time event handling, and lower latency for scenarios like live calls and messaging.
Why Use RELAY for mobile apps?
Low latency and real-time control
RELAY uses WebSockets to maintain active connections between your app and SignalWire’s network, enabling faster event propagation and more responsive user experiences.
Bi-directional communication
With RELAY, your mobile app can both send and receive events in real time — making it ideal for features like incoming calls, messaging notifications, and dynamic call control.
Seamless integration with PSTN and SIP
The SDK supports integration with legacy telephony (PSTN) and SIP endpoints, letting you connect mobile users to phone networks or other VoIP services.
Extendable across use cases
From CRM integrations and enterprise communications to mobile games with live voice or video chat, the RELAY Mobile SDK unlocks real-time interactivity that deepens engagement.
Typical use cases
CRM calling
Build in-app calling that lets users dial contacts or phone numbers directly from a mobile workspace.
Enterprise communications
Embed reliable voice and video calls inside internal tools or team collaboration apps.
In-game voice & video
Add immersive voice and video channels to mobile games for real-time player communication.
Support & helpdesk
Enable real-time contact between users and support agents without disrupting the mobile experience.
How it works — high-level
SignalWire’s RELAY infrastructure uses a persistent connection over WebSockets between the client (your app) and the SignalWire network. Your SDK instance can:
Listen for incoming communications events
Initiate outgoing calls or messaging streams
Route calls to browser, SIP, PSTN, or mobile endpoints
Handle real-time events such as call answered, hangup, or message delivered
At a high level:
Mobile app connects to a RELAY context using WebSocket
RELAY keeps that connection active in the background
Events flow in both directions without polling
Calls, messages, and session state are controlled via SDK methods
Real-world scenarios
Click-to-Call from a mobile CRM
Users tap a phone icon in a mobile CRM app, triggering the RELAY Mobile SDK to dial a contact and connect via PSTN or VoIP.
Integrated video chat
In-app video calls between users — whether 1:1 or part of a room session — with full event feedback for UI updates.
Real-time messaging
Send and receive SMS or app-native chat in real time with push-style responsiveness.
We're excited to see what you will build with these tools. Come and share your experience and bring questions to the SignalWire community!
Frequently asked questions
What is the SignalWire RELAY Mobile SDK?
The RELAY Mobile SDK is a software development kit that lets developers embed real-time voice, video, and messaging into mobile apps using SignalWire’s RELAY APIs, enabling media and PSTN interactions from mobile devices.
How does RELAY differ from older REST-based telecom APIs?
Unlike traditional REST APIs that rely on one-way requests, RELAY uses persistent, asynchronous WebSocket-based connections that support bidirectional signaling and low-latency interactions, making it ideal for real-time in-app communications.
What types of communication can you build with the Mobile SDK?
Developers can build mobile voice and video calling (1-to-1), SIP or WebRTC integration, simultaneous ringing across endpoints, and messaging workflows.
What are common use cases for the SDK?
Typical scenarios include in-app voice/video chat for mobile games, integrated CRM calling on phones, mobile enterprise communication tools, and private, app-driven messaging experiences.
Does the SDK support both inbound and outbound calls?
Yes — the mobile SDK supports both inbound real-time sessions and outbound voice/video calls via RELAY protocols and bridging to PSTN or SIP where configured.
