Asterisk License Information
Asterisk is distributed under the GNU General Public License version 2 and is also available under alternative licenses negotiated directly with Digium, Inc. If you obtained Asterisk under the GPL, then the GPL applies to all loadable Asterisk modules used on your system as well, except as defined below. The GPL (version 2) is included in this source tree in the file COPYING.
This package also includes various components that are not part of Asterisk itself; these components are in the 'contrib' directory and its subdirectories. These components are also distributed under the GPL version 2 as well.
Digium, Inc. (formerly Linux Support Services) holds copyright and/or sufficient licenses to all components of the Asterisk package, and therefore can grant, at its sole discretion, the ability for companies, individuals, or organizations to create proprietary or Open Source (even if not GPL) modules which may be dynamically linked at runtime with the portions of Asterisk which fall under our copyright/license umbrella, or are distributed under more flexible licenses than GPL.
If you wish to use our code in other GPL programs, don't worry - there is no requirement that you provide the same exception in your GPL'd products (although if you've written a module for Asterisk we would strongly encourage you to make the same exception that we do).
Specific permission is also granted to link Asterisk with OpenSSL, OpenH323 and/or the UW IMAP Toolkit and distribute the resulting binary files.
In addition, Asterisk implements two management/control protocols: the Asterisk Manager Interface (AMI) and the Asterisk Gateway Interface (AGI). It is our belief that applications using these protocols to manage or control an Asterisk instance do not have to be licensed under the GPL or a compatible license, as we believe these protocols do not create a 'derivative work' as referred to in the GPL. However, should any court or other judiciary body find that these protocols do fall under the terms of the GPL, then we hereby grant you a license to use these protocols in combination with Asterisk in external applications licensed under any license you wish.
The 'Asterisk' name and logos are trademarks owned by Digium, Inc., and use of them is subject to our trademark licensing policies. If you wish to use these trademarks for purposes other than simple redistribution of Asterisk source code obtained from Digium, you should contact our licensing department to determine the necessary steps you must take. For more information on this policy, please read: http://www.digium.com/en/company/profile/trademarkpolicy.php
If you have any questions regarding our licensing policy, please contact us:
+1.877.344.4861 (via telephone in the USA)
+1.256.428.6000 (via telephone outside the USA)
+1.256.864.0464 (via FAX inside or outside the USA)
IAX2/pbx.digium.com (via IAX2)
email@example.com (via email)
445 Jan Davis Drive NW
Huntsville, AL 35806
Frequently Asked Questions about Licensing
What is an open-source license?
What is the GNU General Public License?
The GPL is a specific open-source license. Reading the preamble at this link is a great introduction, and below that is the full license text.
What if I want to distribute or license Asterisk under a different license?
Digium distributes Asterisk under a multi-licensing model often referred to as Dual-licensing and is additionally made possible by a Contributors License Agreement. This allows Digium to provide Asterisk under licenses other than the GPL. Digium provides information on their alternative commercial licensing at their website.
Some say Dual-licensing is the future of commercial open-source! here is a blog post by Tristan Rhodes and a blog post by Mark Spencer both discussing how dual-licensing is beneficial for open-source projects.
How can I contribute to Asterisk?
Documentation, new features, bug fixes, testing, protocol and programming expertise,, and general feedback are all welcome to the project. There is an overview that points to many resources for developers, also you can see the guidelines for contribution to see how it works.