Whoops. Left out some details in my last reply. Let me try to summarize everything so far.
First, the three hour window I mentioned isn't an exact number and isn't tied to actual calls. I haven't had a 3h+ call since I got the Obihai, so I can't comment on that. However, I have noticed that after *roughly* three hours the device no longer receives incoming calls nor allows me to make outgoing calls. The process is along the following lines: I make a call with the Obihai that works. A couple hours later I get an incoming call that doesn't ring on the Obihai. I check the device and phone light is dark. I try making an outgoing call and I get the "There is no service available to complete your call" message.
Second, dialing "***1" (network stats) always tells me that the Obihai device has the IP I expect and basic networking is fine. That's true regardless of whether I can actually make and receive phone calls.
Third, dialing "**9 222-222-222" (echo test) works perfectly when the phone light is lit and I can make/receive calls. The echo test does *not* work when the phone light is not lit and I am unable to make/receive calls.
Fourth, I tried enabling X_KeepAliveEnable and set X_KeepAliveExpires to 60. That didn't work, so I tried dropping X_KeepAliveExpires down to 30. No luck there either.
Fifth, I tried explicitly setting the DNS servers to the Google DNS servers: 8.8.8.8 and 8.8.4.4. No luck there either.
Sixth, I tried settings the DNS servers *AND* enabling the KeepAlive. That also did not work.