I have a Sprint Motorola Razr with an "extended battery". I use it's cellphone-as-modem feature as my primary internet source now. I use its bluetooth feature to transfer songs, full-length movies and other videos onto it and remove photos and videos I take with the phone to put onto my laptop.
I discovered "Google Maps" for cellphones a few weeks ago and absolutely love it. You can toggle between 2d maps and satellite images, look at traffic flow in select cities, plan routes, pan around maps, etc.
However, it doesn't have GPS capability. Dammit.
I am currently trialing a GPS map/route service (requires monthly subscription) on the phone. The trial lasts 15 days. So far, it has been decent.
Nice features:
1. Turns can be announced via speakerphone and easily heard. I prefer to use the Razr's stereo headphones.
2. You can run the program with the Razr flipped shut. The display shuts down (saving batteries) and you can still hear directions via the speaker (or headphones).
3. It has a "pedestrian" map feature... I haven't trialed this aspect yet, but I'm hoping that it might include bike trails.
4. The GPS seems to work decently. I found one spot (under moderate tree cover) where it couldn't pick up location but has otherwise done fine.
5. If you missed a turn, it would at first give an audible tone, then tell you to do a U-turn (where traffic appropriate). If you missed the u-turn, then the program would recalculate your route based on your current direction (i.e. it would recalculate your route, eliminating the one you passed by).
Disadvantages:
1. There is no easy button to push to have the program repeat verbal directions. You must open the clamshell phone to visualize the next direction.
2. My first attempt at using it driving I had it set to find me the quickest route. It didn't. It pulled up the shortest route... which included a series of dirt roads with speedlimits of 25mph. A mile down the road was a highway with speeds of 55-65mph. I think this would actually be beneficial for biking... but I list it as a disadvantage because it didn't work as stated.
All in all, very nifty setup. If they had a cellphone charger adaptable to a hub generator... I would consider using the GPS feature on an extended tour. I do wish the program was compatible with the iTunes feature... so I could play music and then have the songs interrupted by directions, but I can't see that happening for at least a couple of years.