There is a new navigation software available for the Sony PSP which will leverage the PlaceEngine Wi-Fi geo location services. The software, from Zenrin Map 2 and the Edia MaPlus will remain using the GPS accessory for the PSP, but will add location data that will be provided through Wi-Fi.
This means, for example, if the PSP is connected to a Wi-Fi hotspot the navigation applications can continue to show the location inside buildings where GPS satellites are unreachable.
This GPS receiver for the Sony PSP is only available in Japan. But you can order the PSP-290, The Zenrin Map 2 with GPS and the MaPlus with GPS online. Prices are around $59.90, $95 and $99.90 respectively.