[bjahome]

This happened to me quite a few times (I was trying to pin down the condition that caused the reboot, so the first was a surprise the next five on purpose) this weekend, both with Google nav and Sprint Nav. My conversation caused reboot in under 5 minutes (but not immediately). I have totally stock EVO with the latest OTA update.
At least for me, it happened when my signal was weak or actually roaming. When I was in an area of strong signal, I was able to have a conversation (>10 minutes) with navigation on.
I am not sure if this means the reboot occurred when the map needed updating, and if you are in the boonies with little or no signal, the phone can't handle both the call and map update, but if you have full 3G there is no problems. Either way, it is annoying and should be corrected!