This graphic by Stuart Goldenberg says it all. It refers to the upcoming HP6315 with wifi/cell/bluetooth/infrared et al. David Pogue has written a great little firsthand review for the New York Times. It's called A Palmtop as Wireless Omnivore. The truth that hit home for me is that "when you shop for palmtops...you are really shopping for compromises."
David says that the HP6315, expected out on August 26, switches seamlessly from one brand of wireless to another. But admits that you may look and feel funny using it as a phone. Again, the graphic tells the story here. He says you'll smudge the screen holding it up to your face. I wrote about this PDA/phone myself last Tuesday. Even if you read mine, I gotta say there's more, different and better-written in this NYT piece.