Why does my iPhone Gmail say archive instead of delete?
Apple has added support for Gmail's archive feature with iOS 4. When swiping across a message you wish to delete, the red button that appears says archive instead of delete.
To disable Gmail archiving for an account, follow these steps:
1. Navigate to Settings -> Mail, Contacts, Calendars
2. Select the Gmail account you want to change from archive to delete
3. Touch Archive Messages -> OFF
Now the delete behavior you were used to with iPhone OS 3.x is restored. For those that want to archive their Gmail, the archived messages are hidden from your Inbox. Archived messages can be found in the All Mail folder of your Gmail account.