As a wish list,
Unbreakable and reliable, with a legible display in all lighting conditions and battery, battery, battery, always. Minimum of 2 SD card slots, with 1 full size, to enable simple back-up of SD cards from eg DSLR when travelling, whilst retaining at least 2 SIM slots. Bigger tactile feedback buttons, that can be used whilst wearing gloves, with the option for buttons on the opposite side for us left-handed people. I work in a noisy and dirty environment, so a louder built-in speaker and a more sensitive mic with noise cancellation would be terrific. Infrared, to enable use as a remote. I'll get very optimistic now, and say that a built in laser level and distance meter would be nice. This could go along with terminal points for probes, with built in circuitry to use the phone as a multimeter/storage oscilloscope, but I don't think this is likely A proper headphone jack is important, as I like to use decent headphones when travelling - I travel as light as I can, and more adaptors are just more things to get lost. A line in/out that bypassed the internal headphone amp would be very desirable to enable use as an audio hifi source. Physical HDMI, to enable using the phone as a video source when travelling or for presentations. At this stage, I would take functionality as a worldwide phone or network device as given, really. I've been using a DG700 for years, as it was the most rugged thing I could find at the time that still had some decent functionality, and I haven't managed to break it yet Keep it up.