I had 480 contacts on an ipad that I wanted to delete. The app has the option to select all, so it was as simple as select all> delete. Why Apple does not have this as an option is beyond me. When you have multiple devices using the same account it can be tricky to not affect the other devices when you use iTunes to change content on one device. This app worked for me and I recommend it.
Blueskies238 about Delete Contacts Fast - DeleteQ