Sipdroid: a bare-bones SIP client that lives inside the Android dialer

What the README actually is, and what that tells you

The README.txt in this repository is not a README in the usual sense. It is a copyright header and a history notice, opening with the statement that Sipdroid is an open-source SIP client for Android and pointing to sipdroid.org for more information, then listing four copyright lines: the Sipdroid Open Source Project in 2009, Hughes Systique Corporation in 2008, the Android Open Source Project in 2006, and Luca Veltri of the University of Parma in 2005. It carries the full GPL notice and the standard warranty disclaimer. That is the entire documentation content, which tells you something useful about the project: it is old, it is a chain of inherited code rather than a fresh design, and the project site is the documentation. Anyone evaluating it should treat sipdroid.org and the source tree as the documentation set, and this repository as the code.

The line back to Mjsip and the Android port

The README explains the lineage in three bullets, and the lineage explains the architecture. The source code was based on Mjsip, which contributed the original stack and the packages org.zoolu.*, and on Hughes Systique Corporation, which did the initial port and development of a test SIP client for the Android platform with the packages org.sipdroid.*. Then the Sipdroid Open Source project began with porting to an actual phone, the Android Developer Phone 1, and testing basic calls, which is also why patches to the Android Frameworks were submitted. Work then began on features like putting calls on hold, muting, sending DTMF and handing off between networks. The two package roots, org.zoolu and org.sipdroid, are the seam to look at when you read the source, because a stack protocol implementation from a university in Italy and an Android port from a US company sit underneath the app you actually run.

The dialer integration is the product, and it is under-documented

The README states that, as the copyright notes indicate, most modules in org.sipdroid.ui.* were added to fully integrate the client into Android's built-in dialer, so that the standard UI can be used to initiate calls or ring. That is the distinguishing feature of Sipdroid compared with a standalone SIP app with its own account screen, contact list and keypad. The cost of that design is that a large part of the interesting behaviour lives in the platform's dialer rather than in the app, and the repository does not document how that integration is configured, which intents it registers or what a device vendor's changes to the dialer do to it. If you are evaluating this, the questions to answer are about the dialer, not about SIP: how accounts appear in the dialer, whether the contact picker integrates, and what happens on a device where the OEM dialer is not the AOSP one.

Building the app from the Gradle project

The repository is an Android application project rather than a library. The top level carries build.gradle, settings.gradle and gradle.properties, an app/ directory holding the application module, and a set of text files: README.txt, BUILD.txt, CHANGELOG.TXT, LICENSE.TXT and ADDITIONAL_TERMS.txt, plus a.gitignore. The primary language of the repository is C, which is consistent with the inherited Mjsip stack, while the Android side and the user interface packages are Java. The documentation in the repository does not give a build command, so there is nothing to copy here. The build description is in BUILD.txt and the dependency and version declarations are in the Gradle files, and the application module in app/ is where the packaging settings live. Anyone building it needs a working Android SDK and Gradle toolchain matched to the Gradle version the project pins, and there is no container recipe or CI definition in the repository to lean on.

Version history: 6.5 in 2024, and a branch that still moves

The published versions are old relative to the repository activity. The recent releases are 6.5, tagged on 2024-07-01, and 6.3, tagged on 2022-11-08, with a gap of more than a year between those two points. The repository itself is not archived, and the last push was on 2026-07-06, so commits are landing on the master branch without producing a new tag. For a user installing the app, that distinction matters: the artefact you can obtain is 6.5, and whatever is on the branch has not been versioned or, as far as the repository says, tested as a release. CHANGELOG.TXT is where the differences between those points are recorded, and it is the first file to read when you need to know whether a fix you need landed after 6.5.

GPL-3.0 plus an additional terms file

The licensing needs two files read, not one. LICENSE.TXT holds the GNU General Public License, and the README's notice spells out the standard either version 3 of the License or, at your option, any later version. That is the permissive-in-form GPL-3.0-or-later framing, and it is the licence a distributor works with. Alongside it the repository carries ADDITIONAL_TERMS.txt, a file whose presence means the project layers other conditions on top of the GPL. What those additional terms cover is not described in the README, and they are the part of the licence picture that determines what a commercial distributor, a carrier integrating the client, or a vendor shipping it inside another application may actually do. Read both files before you build a distribution, and treat the additional terms as the operative question rather than the GPL itself.

Where a different client is the better answer

Two situations point elsewhere. The first is a business handset deployment that needs provisioning, support and a signed build, because Sipdroid gives you a GPL codebase with an open source project behind it, an additional terms file, and a release history whose newest tag is 6.5 from 2024-07-01, which is not a support contract. The second is a user who wants a modern softphone with push notifications, video calling and a contact sync that works with the current account framework, since the feature list in the README stops at hold, mute, DTMF and network handover, all described as work that had begun. The genuine alternative here is not another open source client with the same goals but a different codebase; it is the platform's own SIP stack, since the app is built on the Mjsip stack and the dialer integration is a platform feature rather than a client feature. If what you need is a phone that can place a SIP call from the home screen, that platform route already covers it without shipping an APK.

Editorial conclusion

Sipdroid fits a developer who needs to place SIP calls from an Android device without a proprietary client, and who is prepared to read the source, since the README in the repository is a copyright and history notice rather than a user guide, and the dialer integration that defines the project is not documented in the repository at all. It does not fit a product team that needs vendor support, a signed release process or a modern Android build story, since the most recent tag is 6.5 from 2024-07-01 while the last push was on 2026-07-06. Before you build on it, read ADDITIONAL_TERMS.txt next to LICENSE.TXT to see what the additional terms change, and read CHANGELOG.TXT to work out what has changed since the 6.5 release you would actually be installing.

Frequently asked questions

Official sources

1. i-p-tel/sipdroid on GitHub
2. License: GPL-3.0
3. Project website
4. README
5. Releases