3D buildings on GPS displays using Tele Atlas' new 3d masp should be arriving in "All In One" gps devices near the end of the year. I believe MIO showed one of at a trade show in Asia recently, but I can't find the article to reference.
There technology is definitely there. I have a nearly 2 year old Dell PDA with a 624 Mhz processor and a hardware 3D graphics accelerator (Axim X50v)
http://www.gpsreview.net/3d-mapping-from-tele-atlas/