I have a cell phone/PDA combo from Samsung. It's got Palm OS on it, to boot. DH just upgraded his to one with MS Windows.
My only complaint is that I can no longer beam calendar updates to him!
But yes, I never leave home without mine. I love being in the doctor's office and when the receptionist says "shall we reschedule for another four weeks?" being able to whip out both mine and DH's calendar and knowing precisely whether or not four weeks from today is still free.