How to delete Android contacts at once? can you help me delete my contacts at once? I don't want to spend my whole day deleting them one by one. can you suggest a free application for me to use? thanks
The simple way to do this is to use Duplicate Contacts. 
Although it is meant for duplicate contacts, it also manages other contacts as well that are stored in your different accounts, including deleting all of them if you wish

Deleted contacts are stored as a .vcf file in the root of sd card storage.

Its general description is:


  Simple tool to see and delete duplicate contacts. You can see a list
  of contacts sorted by name or by number and you can select which to
  delete. The duplicate contacts are automatically selected. The removed
  contacts are saved on vcf file on sdcard.


From experience this is one of the very few  applications that serves its purpose - to delete and NOT to merge contacts.