I was looking for a way to shoot startrails on my N920 and finally stumbled on CameraPro (and I cannot recommend it enough!).
Took 135 photos using the 'Timelapse' option on 4 second exposure, f/2, ISO1600. Then merged them together using a desktop app called 'startrails' which you can get from startrails.de.
Ive taken a few of these shots with my Canon and considering this is from a phone I am quite happy with the result. It might be very, very, very gradual motion, but motion all the same!