Yes, you can.... phone uses 2g network to manage voice calls and 3g to internet traffic.

But in my case, my weekend home is on a small town, with average 3g signal. Furthermore my house is stone built, massive stone walls. So I only have 3g signal on a room of the first level, while I usually work on floor level. So I forward my calls to my home phone which is next to me, in order to avoid climbing stairs and running to the room where I have the N900 working as a wifi hotspot.

Yes, I know is a little bit of a mess.

By the way, run for the Joikuspot. It's unvaluable, and now it's only at 5 € on ovi store. I paid 9 for mine (although you can find it free on the net if you want...). I never have regreated of buying it.