Regarding bandwidth, since that is probably the most important resource required by your voice servers: do you strategically use the mixed-calculation-type pricing that some dedicated server providers offer (where you can get large amounts of traffic included in cheap server prices because very few heavy users are subsidized by many users that only use a tiny fraction of their bandwidth share) or are you rather renting dedicated uplinks for your servers that you and your provider expect to be fully saturated most of the time?