Exact same problem has come up on my oBI1062 on all google voice configured lines.
I just upgraded to latest firmware (OBiPhone-5-1-8-4643.fw) but problem persists.
This is not specific to Obi though. I have the same symptom come up this week, on
FreePBX Google Motif plugin. It has one way audio as well. Google has made some
changes but failed to tell the world. The one way audio only occurs during outbound calls.
Inbound calls work just fine.