The HP iPaq rx5900 Travel Companion is a PDA with GPS. It has the software from the TomTom GPS and a windscreen mount for a car. This a somewhat uncomfortable compromise being expensive for a small screen (3.5 inch) GPS unit and low resolution (QVGA 320 x 240) compared to newer PDAs.
There is a merging of functions happening with PDAs, GPS units, handled games and phones. Exactly what functions get incorporated depends more on what makes sense to the buyer, than what is possible with the technololgy.