I have a Kindle 2 with cellular access. I used it for GMail communication while bicycling down the Pacific Coast last year. Rendering glitches aside, it's tolerable for reading email, though writing takes a ridiculously long time due to screen redraws. Also, it absolutely sucks battery life down if you do much writing. I can't imagine using it for chatting, and I don't know how GVoice could be used at all.

Unless the Kindle 3 is radically different, I can't see how it would be a significantly different experience.