The 'domes' that I see on top of tractor-trailers verifies what I think I know - that they've been doing this for years in the trucking industry - at least here in the US. The dome is a GPS antenna and if I am not mistaken the system reports via satellite, cell phone or local VHF/UHF link.
Amateur radio operators have their own APRS - Automated Position Reporting System. Take a look in current ham radio publications for info. A recent copy of QST published by ARRL details a relatively simple project where a simple hand-held GPS unit is interfaced with a hand-held ham transceiver. I presume that a similar unit (or many more) exists to recieve and process the data.