Dunno about the N9 but the N950 got superb voice quality so I wouldn't worry about that. The N9 beeing made in plastic is said to have very good reception too.
When I run on into a small forest on the route, keeping Nokia N9 still holds full 3G coverage. All other phones I’ve tested, jump here on the 2G network, but even in the midst of the forest, Nokia N9 has no problem keeping 3G. I get around 6 Mbit / s speed of Nokia N9 in this area, it’s crazy!