I seldom use my mobile to call people but mostly use data services and personal organiser features. My mobile has all but replaced my PDA but what I really want it to replace is my laptop.
My ideal mobile would have a projector keyboard so that I can enter data easily and a projector display so that it would not be constrained by the size of the phone. It would have a productivity suite of applications compatible with microsoft office and, of course, email and instant messaging. On the connectivity side bluetooth, WLAN, 3G, all bands and not forgetting IRDA (its amazing how many devices don't have this these days but I still find myself in situations where it is the only option).
My ideal mobile will have a battery that will last for two weeks on standby and at least three days of heavy use. A large amount of internal memory would be good but also support for memory cards is essential. I use the radio on my phone a fair bit so throw that in too. A camera will be essential for video calls. When placed on a desk it will turn the whole surface area of the desk in to a giant speaker for some decent sound.
Basically I want my mobile to do everything.