I would say that the latency would be fine for running VOIP. We are also running MPLS between a few sites and I just checked one of them and the response time was between 50 and 60ms. We have a few jobsites that arent using MPLS but rather a DSL connection with a site to site VPN that have latencies up into the 100ms range and we are running CIsco VOIP phones at those sites as well.