We've recenlty completed upgrading ALL our VoIP infrastructure to RAID 1 and RAID10 SSD arrays at our tier 4 datacentre. In addition we have now enabled Opus codec support and also SLN24 to allow a much wider sampling range for HD/Ultra Wideband phone calls and for IVR/recordings in 24khz. Here at VSIP we are truly HD-Ready!
While we still think speex is a great codec to use for VoIP, opus is even better all-round and has become our new favorite. Handles packet loss even better than speex thanks to packet loss concealment and good loss robustness. We reccomend you use opus where possible.
For more information on the Opus codec see http://opus-codec.org