First of all, N9 is awesome, and true, i'll not trade it for anything else

1. Its a phone a great one, will do this. It lacks smart dial though
2. Sure. It has whatsup for that, which many will agree is in many ways better than official WhatsApp. But also a little unstable.
3. Call quality is good. No problem there.. The only problem i had with calls is that the earpiece is small. When i switched from C7(has a bigger earpice) to N9 i had some trouble positioning it against my ear. That's no problem now
4. It does have a decent battery life. I used to get around 3+ hrs of screen-on time along with 15+ hrs of idle time when i used it as my daily driver. Now that i don't, I get around 1+ hr screen-on along with 2+ days to total standby.
5. Maps is great on N9. But i wouldn't suggest browsing the net on N9. YouTube is also great with cutetube.

N9 doesn't play 720p videos, slows down sometimes and using whatsup for a long time eats up a lot of ram, and it gets laggy, a lot. But i cannot imagine leaving N9 just for these reasons. I've learnt many things about linux while exploring the N9. And the UI is the best i've used so far, love it.

In the end i would say that, if you are going to do mostly just this then N9 will do it, but lumia 800 might do it better. but there is a lot of stuff that N9 can do and lumia 800 cannot.