Do not take the 150ms as an hard limit all the time.
I was on a skype conversation yesterday that had an average roundtrip of about 1 sec, plus the peer-to-peer routing by skype that I'm unable to evaluate. We were able keep an almost normal conversation after all, altought at the same time the delay was noticeable. I routinely call across the Ocean with a cisco solution and you cannot tell the difference with calling next room
I think that the time the recommendations were written, no advantaged de-jitter and echo cancellation algorithms were largely available as today. I find that they do an excellent job at concealing delay, packet loss, etc.
