As soon as you are not distributing it, you can use it internally
for your commercial activities (you must let you users access the
source code, according to the GPLv3 licence).
See more at https://www.linphone.org/licensing-services
However, if you plan to distribute it, your must rebrand
(white-label) the application (even with the GPLv3 licence) .
We do sell this service.
We also sell proprietary licences, allowing you to hide the source
code. This comes with 6 months of included support.