Yealink SIP-T21 - Manual (Page 4)

Yealink SIP-T21P/SIP-T21 firmware contains third-party software under the GNU General Public License (GPL).
Yealink uses software under the specific terms of the GPL. Please refer to the GPL for the exact terms and
conditions of the license.
The original GPL license, source code of components licensed under GPL and used in Yealink products can
be downloaded online:
http://www.yealink.com/GPLOpenSource.aspx?BaseInfoCateId=293&NewsCateId=293&CateId=293 .