So is it TomTom you've got? I thought you had NavMan.

How much data will TomTom traffic will shift over GPRS then it's connected? If you're paying by the MB a long journey could wind up being quite expensive. What happens if the phone rings whilst you're navigating? Will it take over the whole screen or will TomTom fight to be at the top of the z order? I've found the GPS screen pops up with annoying regularity if my GPS isn't connected.

EDIT: So has the XDA got a GPS receiver as well?