Thank you so much. That is what I wanted to hear. It confirms what I think I saw via wireshark.
My goal was to make an end to end encrypted phone call using off the shelf phones. Here is what I did.
I took a TinyHardwareFirewall (from the website of the same name) and connected it to my macbook. The THF has a wifi radio and an Ethernet port. The THF wifi is associated to an access point that goes to the Internet through a DSL modem.
The THF Ethernet port is plugged into an Ethernet switch. It feeds everything on the switch dhcp. The laptop wifi is off and both it and an obi 100 are also plugged into the Ethernet switch. A regular phone is plugged into the obi, and the obi is powered off.
I then instruct the THF to connect to the VPN (256bit openvpn) and verify Internet connectivity with the laptop. Then I power on the Obi. It connects and is happy.
I then walk into the next room where the setup is duplicated with the following changes: obi 110 instead of 100, I use my iPhone in personal hotspot mode as an access point for this THF, and I use my Ubuntu laptop. Another regular phone is plugged in here.
I make sure to connect to the same vpn server as before and turn on the Obi 110.
Here I should note that both Obi's have been previously registered on ObiTalk network.
I can make calls from one to the other via the 9 digit number on the bottom of each unit. It sounds much better than I thought it would, great in fact, and it seems that with the exception of registration and signaling all voice data is fully encrypted end to end.
I am very happy. I have done this before with other voip products but it required a LOT more hardware, software, time, effort and money. I can fit all of this in my laptop case and it took less than an hour from unboxing to talking.
Full disclosure: I am the president and founder of HotSpotVPN and TinyHardwareFirewall. I have no ties with Obi other than being a happy customer.