Searched for this and couldn't find an answer...it's possible I didn't search hard enough though. What happens if you're using google nav and you lose 3G signal. Does the whole thing stop? I mean, the GPS should still be working, so it should still know where you are. Does the phone cache the exact route when you're using the phone, so the GPS can take over if you lose signal. And in that case, shouldn't you just turn off your 3g after starting the route to save battery?