>>>Any point in the US is within 25ms RTT (or less) of a major exchange; eliminating this 25ms of latency will have no effect on VoIP unless you're already near the 250ms RTT limit for other reasons.<<<

25 MS is assuming that the only delay is due to the speed of light. Add equipment, especially routers or other gear that requires manipulating packets and the delays add up quickly. I once read that the most people wil tolerate on a regular basis is around 150-180 ms. I think that is much too high for regular use