Because of the overt agenda involved, I'm normally quite skeptical of vendor-written articles about VoIP. I usually don't waste my time reading them, nor your time linking to them.
I will make an exception for a piece entitled "Assuring VoIP Quality for Triple Play: It's a Whole New Ballgame." Written by two executives at IP performance analysis tools provider Spirent Communications, the piece in the current issue of Converge! Network Digest offers VoIP carriers strategic post-deployment analytic advice that goes beyond the numbers. Stuff such as how to decide which network application layer a quality of call issue should be looked at most closely.
You don't have to be a carrier to benefit from this piece. The information is general enough to apply to enterprise network VoIP as well.