I have an unlocked Vodafone Blackberry Bold in Shanghai. No problems with it or GPS. I use Google Maps, it downloads maps in Chinese. (I heard Google used to have English maps during the Olympics, but now only has Chinese accessible here.) I can't read Chinese easily and quickly, but here are some tips on using Google Maps (it rocks!):
1. the app runs in English, only the maps/street names/landmarks/subway is in Chinese. so the app itself is very usable.
2. I'm surprised at how useful even Chinese maps are. I can find my way around easily -- Shanghai is really not built on a "grid" type road system -- so I can tell where I am by the shapes of roads. The big name streets I can read Nanjing Lu, Huaihai Lu, and you should learn the major roads wherever you are in local language anyway.
3. Taxi drivers can read the maps and take you where you want to go. This is a key feature -- how to communicate destinations with taxi drivers is an issue.
4. BIG TIP: by moving your cursor and clicking on the map (on the Bold I use the trackball), a menu pops up. At the top of the menu, the Google Map app loads the location's address in Pinyin/English. So, while you can't get the map in Pinyin/English, you can get specific locations. Which fits my needs 95% of the time.
5. Google Maps has a cool traffic function that helps keep me out of traffic jams. I've had good luck with its accuracy during rush hour.
So I give Google Maps in China a rating of 4 out of 5 Shao Long Bao. It would get 5 if it were selectable in English...
I also use GPS logger to track path data, elevation, speed, etc. when I'm in a geeky mood.
But Google Maps is your answer.