A fair few of the new S60 phones, such as the Nokia N95 come with a GPS receiver built in. But what about us schmuck without GPS receivers?
Back when I had my old Nokia 8250, there was a hidden menu item that let you check out some of the internals of the phone. One of the things you could do was see what cell towers the phone was connected to. Off the top of my head, in the average city area, the phone would maintain connections with around 8 GSM cell towers.
So here's a idea: Nokia creates a GPS driver for its Symbian OS (S60) that uses the IDs of the GSM cell towers you're connected to in order to determine your position, in the absence of GPS. It should be pretty easy to figure out your location to within a few city blocks using only 3 cell towers. For more remote locations (like a highway), the resolution would of course be poorer, but hey, it's better than having nothing at all, right?