Q: How can I delete all contacts on iPhone 4?

you leave them pressed then you press delete or delete them from your computer

un fortunatly u can only do it from a computer..

You can mass delete by re-synching ‘Contacts’ in the ‘Advanced’ section of the Info tab in iTunes. Select Contacts under the ‘Replace information on this iPhone’, click Apply and re-sync.

Yeah you can only do all with itunes.

On the phone itself you can only delete one at a time.

Go to the contact, choose edit, scroll down, at the bottom is a delete option.

If you have them syncing with another source (gmail, windows contacts, Yahoo, etc.) then in iTunes, select your iPhone under devices (left side), go to Info (top), deselect "Sync contacts with".

When you do this, it will ask you to remove your contacts or not.  Click on "Remove Contacts", and then Apply (botton right).

If you don't have your contacts sync'd, then you can either setup a temporary sync to what service you have access to and then do the above, or do them one at a time.

Thank you!!!  This "Remove Contacts" process through iTunes worked for me.  Now I am planning on syncing with my Google Contacts since that list is all cleaned up.

There is an easier way than using iTunes. I know everyone here has there problem solved now but I stumbled accorss this thread while searching for how to delete all on Google. If When someone else searches the same they will find this way most preferable if they are away from their PC or have a PC-less iOS 5 device.

Here is how to do it.:

1. Open the Settings application on your device's home screen.

2. Open Mail, Contacts, Calendars.

3. Press Add Account....

4. Select Microsoft Exchange. iOS 4.0+ allows multiple Exchange accounts. However, if you're on a device that doesn't let you add a second account, you could also use CalDAV to sync Google Calendar and IMAPto sync Gmail.

Enter Account Info

5. In the Email field, enter your full Google Account email address. If you use an @googlemail.com address, you may see an "Unable to verify certificate" warning when you proceed to the next step.

6. Leave the Domain field blank.

7. Enter your full Google Account email address as the Username.

8. Enter your Google Account password as the Password.

Notes about passwords:

• Be sure that you have a strong password for your Google Account.
• If you see an error message saying "Invalid Password", you may need to unlock your account by solving a short CAPTCHA. Go to https://www.google.com/accounts/UnlockCaptcha.
• If you are a 2-step verification user, please use an application-specific password instead of your regular password in this field.

9. Tap Next at the top of your screen.

9a. Choose Cancel if the Unable to Verify Certificate dialog appears.

10. When the new Server field appears, enter m.google.com.

11. Press Next at the top of your screen again.

    < ------------LOOK!!!! Just click delete and move on. Make sure that the place you are syncing with either

1. Has no contacts in (if you want nothing in your contact book on iPhone)
   
2. Has ALL the contacts which you want on your iPhone
   

But what happens after you then resync your iPhone with iTunes?  Surely all those contacts on your computer will then reappear on your phone again and you will have a merged list?

Try "LöschenQ" from the AppStore. You can delete all contacts without iTunes.

I downloaded an app called Easy Delete shortly after posting my last comment, so yes it is now sorted.  This really should be a basic feature in the iphone settings.

Now that I have cleaned up the contacts, what happens if I sync it now with iTunes?  Will they all repapear again or delete from the mac too?

Easiest thing is to download an app from the Store.  It will save you tons of time.  I have been dealing with this problem since I got my phone in October.  I would spend hours deleting contacts and then they would pop right back up again.  I got DeleteQ for 99 cents and that worked awesome.  I have all my contacts updated on my laptop in my address book. Once you delete all your contacts using the app just go in the advanced setting on the info tab and have it replace information on your phone.  Then if you don't want to do that again, just uncheck the box. 

And why isn't there a button for deleting all contacts right on the phone?

I think my easiest way is:

1-settings

2-mail,contacts

3-choose from the Accounts the one you want to delete its contacts from your iphone for example Yahoo.

4-then you just switch the contacts OFF.

5-then press delete from my iphone.

There you have it.

Download an app called easy backup from AppStore.....

1 go to sources...

2 then choose the contact source which you want.....

3 then select which contacts you want to delete....

4 then press the delete icon.....

Four easy steps!!!!!!!!!!