If you wish to delete all contacts from your Android device, there is a quicker way than deleting them one-by-one. Just use one of these methods.
Method 1 – Clear data on the device
1. Disable syncing by going to Settings > Accounts & sync. Select your Google account and uncheck Contacts. If you sync contacts with other apps such as Facebook or Twitter, be sure to disable syncing for those apps as well.
2. Go to Settings > Applications > Manage applications > All > Contacts Storage and select Clear data.
Note: This will also clear other data like your recent calls and Favorites.
Method 2 – Delete all contacts from the account you sync with
If you don’t mind losing your contacts in your account as well as your phone, delete all of the contacts from the account your Android syncs with using your computer. For example, if you sync your Android with Google Contacts, sign into Gmail and follow these steps:
1. Select Contacts on the left pane.
2. Check the box at the top of the left row to select all contacts.
3. Select More > Delete contacts.
The next time your Android automatically syncs with Google, they will be completely cleared.