Is there a voice open source engine for one-way broadcasting of speech to clients?

Question

SIP

There is a server part of the game, there are about 300-700 people online. There is a desire to bring a voice component to the game: to report commands, to control players. The first and minimal part: broadcast the voice of one person to all players.
What is: ms server, ms sql database.
Where to look, what to read about? I guess it's something like Internet radio on IceCast2 or ShoutCast, is it?