If you have a dedicated server, you might consider to install trixbox. You can ask your vendor to download trixbox from its website, burn to a CD and install from there. It's the easiest way.
Or you might want to consider to get a VPS, install trixbox on it, then upgrade to dedicated server when needed. I only have experience on Xen VPS, so I am not sure about other platform, but I have seen someone using trixbox on OpenVZ too.
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