You assume Verizon, I would not single Google out for this bug because in my opinion they never got the software TB compatible even after update.. Try disable 4G and see if it works on 3G, if it does then they may not configured the software to see and use the 4G connection.
I did some testing with my room mate and my phone. We both have Thunderbolts. We tried several different scenarios:
Both on 4G or 3G
Every time one of us tried to call the other one, it would kill our network connection (4G or 3G).
Both on seperate WiFi
This worked a little better. When we tried calling eachother, it would connect for about 1 second, then disconnect.
Both on the same WiFi
This worked fine.
I was able to get a vide chat session from my TB to my fiancee's laptop Sunday morning. We were both connected to the same wifi network. The results were turrible. It probably took 5 attempts to connect. Video was choppy and there was a lag between our devices.
Have not tried since.