This has only happened to me once, and it was over a month ago right when I first got the phone, but I'd swear I remember that that during the call, when it came time to take my exit, the voice navigation came through the earpiece telling me to turn then returned to the call.
edit: too slow typin my response... hmm apparently I'm remembering incorrectly then. Man, cocaine's a helluva drug... :laugh:
2nd edit: I thought I've heard that when you use navigation, it loads your route for you and you can continue to follow it/get directions, even if you lose signal (the maps will no longer be able to update your view, but the actual programmed route will still be available). Wouldn't this mean, in theory, that even though you aren't receiving data while on a call, the directions for your route could still be going?