but gmxt need its own GP10x to work.

I havent got myself a Standalone GPSr, but as far as i am using my PDA GPS, its all good though. No doubt while halfway navigating and a call interupt maybe bad, but you could always close the call window and it will return back to the navigation screen while you still have your call.

screen might be small, but dont tell you are looking at the gps screen and drive. it is recommended to listen to the instruction and possibly just a glimpse. Processor wise, from my HP 6965(416mhz) to P535(520mhz), both perform well in either mapking or garmin que. Only let down is battery draining, so you must have an in car charger.

GPRS download? I only know they use to download the datas of the satellites and it is manual download. Usually it is for Assisted GPS for faster locking time.