Bwin has an Iphone App for real money, so there is a good chance that Party Poker will have one also at some point (since they are merging)
They do not currently, no, although I believe they are hoping to expand. Apart from that there is really nothing for US players on the iPhone unless you download an app which allows you to control your computer from your iPhone. I forget what it is called right now but I'm sure someone can tell you...
I think there might be too many problems with drop-out and signal issues for it to work properly. Though on a separate issue, I'm surprised none of the big sites have made their sites available through the Playstation network or equivalent Xbox network. I would imagine this is an untapped resource so far, and no doubt highly profitable.