We have 300 extension PABX that is dying. We want to replace it with a VoIP-capable syste, but not implement VoIP until we have reduced bandwith use and purchased more capacity. (Don't suggest "buy it now and it will pay for itself". We are a charity, so conventional ROI calculations go out of the window.) We'd like to keep the existing 300 digital handsets, and down the track migrate to soft phones and headsets. Is this a) feasible b) sensible ?