In preperation for a trip to Munich in a few weeks I have used the Google maps application to look for and bookmark places to visit as well as my hotel.
I searched for locations on my MacBook air and then emailed them to myself. Once the link is opened on the phone I was able to save the location for later recall.
I also found an iPhone friendly website, www.medd44.com/metro/ that has PDF’s of all the major city undergrounds.