I did not read the full T&C when I made the connection on GoGo's page. But I agree that voice calls would be annoying and I don't endorse that they be allowed (even though it's technically impractical with the upload speeds), but my exercise proved that the traffic is getting past the firewall policies at least in the case of using GoogleTalk via the iChat app. Different IM clients (which almost all support voice and video) use different ports and protocols, so it's possible other chat/IM clients wouldn't work at all.