From what I checked it seems I was right - all communication between Obitalk points done through the relay gateway 204.236.134.243 - i.e. ObiTalk server at Amazon cloud.
Even if you open a ports for inbound connections to your ObiGV, it will still use a relay server for RTP data if you call from outside your private network, i.e. from iPhone ObiOn application over 3G. If you are on the same LAN, ObiTalk seems to understand this and then no relay is used.
I do not know where exactly server is hosted (Virginia or N California) but while it may be less significant to US users, for users abroad it can add a significant latency.
However, ObiHai is a new company and I hope they will get enough funds to continue and develop there network. By now - I am very pleased with the device functionality, it does exactly what I need !