Halcyon

What Halcyon is

Halcyon is an Android softphone for SIP calling through a PBX. Built on PJSIP and integrated with Android Telecom, it can register over UDP, TCP or TLS. Users can keep multiple SIP identities side by side and choose an account for each call. When server-side push is configured, the registrar sends a data-only FCM message before an incoming call to wake the device; Halcyon advertises RFC 8599 push parameters.

Its self-managed Android ConnectionService handles tel: and sip: calls, including from the lock screen. Telecom-native audio routing supports Bluetooth headsets and Android Auto. The listed audio codecs are Opus, G.722, AMR-WB and G.729; video codecs are VP8, VP9 and arm64 MediaCodec H.264. SRTP encrypted media is listed, while ZRTP support is on the roadmap.

Halcyon is described as self-hostable, with the user's PBX connecting directly to FCM and no third-party push relay in the call path. Without server-side push, it falls back to a foreground SIP service with a permanent TLS registration, which has the usual battery cost. The project is pre-1.0 and in active development. Signed APK builds are available from GitHub Releases, and a Play Store listing is planned for the first stable release. It is free to install and use during pre-1.0 development; pricing and licensing for 1.0 will be announced before launch.

Who it suits

Halcyon suits Android users who make SIP calls through a PBX and want multiple SIP identities available on one device. It is also for people prepared to configure server-side push or use the foreground service, and who are comfortable with pre-1.0 software.

Limits

The pre-1.0 plan is free to install and use; pricing and licensing for 1.0 will be announced before launch. Without server-side push, incoming calls rely on a foreground SIP service with a permanent TLS registration and its usual battery cost. Video codecs are currently compiled only into the arm64-v8a build.

Getting started

1. Visit the Halcyon website.
2. Use Android 8.0 (API 26) or newer on a supported arm64-v8a, armeabi-v7a or x86_64 device.
3. Get a signed APK build from GitHub Releases.
4. Configure the PBX for UDP, TCP or TLS registration.
5. Configure server-side push through FCM if you want push wake-up for incoming calls.
6. Add SIP identities and select an account for calls.

Verdict

Pick Halcyon if you need a free, Android-based SIP softphone and can work with its pre-1.0 status and PBX setup. Server-side push supports device wake-up for incoming calls; without it, the foreground service has a battery cost. Look elsewhere if you need iOS or a stable 1.0 release today.