I am also not at all an expert in GPL licencing or IP, but would like to
add that any customisation you make specifically for the purpose of
interacting with a billing server or other external application is
likely to take the form of a Kamailio module, rather than modifications
to the existing Kamailio modules, the Kamailio core, or any other part
of the stock code tree.
As far as I know, under the GPL--broadly speaking, for I certainly don't
know or remember the specifics--modules get different treatment than
modifications per se.
As far sa I know, if you can stick your code into [a] completely
self-contained module(s) (and given what you've said about what
specifically you want to accomplish, it seems to me that you absolutely
can) that interact(s) with Kamailio using its module APIs and requires
no modifications to Kamailio itself, it's not subject to the same
licence constraints as modifications per se.
Please do not take my advice as stated, and consult a competent
software/IP attorney.
-- Alex
--
Alex Balashov - Principal
Evariste Systems LLC
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