Does this wipe the phone numbers /contacts... or just the junk from using apps/ internet/ect
A cache wipe shouldn't erase any of your data (be careful in choosing from the menu, though, because a factory data reset will delete all your data).
One thing that I'll to add this as a heads-up! On doing a cache clear there can be time limit on between the button presses it could range from 5sec. to 10sec. but once it passes the time limit the process of running the cache will have to be reran.. Hope this helps.. b33