Ventrilo (English Wikipedia)

"Copyright Infringement: Flagship Industries, Inc. v. John Doe". Illinois Southern District Court: RFC Express. 2 May 2008. Archived from the original on 28 June 2013. Retrieved 25 February 2013. Court Case Number: 3:08-cv-00327-GPM-DGW
"Copyright Infringement: Flagship Industries, Inc. v. John Doe". Illinois Northern District Court: RFC Express. 6 March 2009. Archived from the original on 28 June 2013. Retrieved 25 February 2013. Court Case Number: 1:09-cv-01429

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So How many users can I have? (Ventrilo Tech Support)
"Ventrilo Linux/ Unix client Pending Release". Ventrilo Tech Support. 30 May 2005. Retrieved 25 February 2013. The Ventrilo / Linux client tech support forum is here pending the official release of the client. At the current time we do not have an official release date. Once we do it will be posted here...

"Copyright Infringement: Flagship Industries, Inc. v. John Doe". Illinois Southern District Court: RFC Express. 2 May 2008. Archived from the original on 28 June 2013. Retrieved 25 February 2013. Court Case Number: 3:08-cv-00327-GPM-DGW
"Copyright Infringement: Flagship Industries, Inc. v. John Doe". Illinois Northern District Court: RFC Express. 6 March 2009. Archived from the original on 28 June 2013. Retrieved 25 February 2013. Court Case Number: 1:09-cv-01429