In a nutshell, PJSIP is released under dual-license scheme, namely GPL and proprietary license.
PJSIP may be linked with bundled or external third-party software, most of them are open source, but some may require specific licensing terms.
Below are more detailed terms of PJSIP license.
PJSIP software (”the SOFTWARE”) consists of:
A cross-platforms portability and framework library
An adjunct library to pjlib which provides various utility functions
A NAT traversal helper library
A multimedia communications library
A SIP protocol stack collections
High level C user agent library
High level C++/Java/Python/SWIG user agent library
and any and all build scripts, makefiles, tools, samples, and/or applications available and/or required to use or modify such software.
The SOFTWARE may provide links to third party libraries or code (collectively “Third Party Software”) to implement various functions, and access to Third Party Software may be included along with the SOFTWARE delivery as a convenience. Third Party Software does not comprise part of the SOFTWARE.
The SOFTWARE is released under dual license, open source (GPL) or an alternative license.
The SOFTWARE may be used according to Free Software GNU General Public License (GPL) version 2, or (at your option) any later version, with special exception to permit linking with some Open Source Third Party libraries set out in the following section.
The GPL allows you to compile, modify, link, or combine the SOFTWARE with other software, commercial or non-commercial, as long as the resulting program complies with GPL (see the GPL Compliance Guide for what this means). Copy of GNU General Public License is available on the http://www.gnu.org. More information about GPL can be found in GPL FAQ.
If you can’t comply with GPL, an alternative licensing scheme may be arranged. The alternative license also comes with technical support directly from PJSIP authors.
If you still have questions, just email firstname.lastname@example.org and we’ll help you sort it out.
As a special exception to GPL, the author of the SOFTWARE gives permission to link the SOFTWARE with Open Source Third Party Software in the following section, and distribute the linked combinations. GNU General Public License must be obeyed in all respects for all of the code used other than those Third Party Software.
Third Party Software Licensing Requirements
In addition to the licensing requirements of the SOFTWARE, you must make sure that your software meets the licensing requirements of the third party libraries in the following section. Some third party libraries may require attributions to be placed in the SOFTWARE, significant portion of the SOFTWARE, and/or in the accompanying documentation.