I changed one of my gmail (Apps for Your Domain) accounts from the standard iOS gmail setup to an Exchange service. I did this primarily for push calendar syncing, but I noticed that following the change the iOS Mail app appeared different in subtle ways. In particular, the Archive icon was gone from my iPhone toolbar, replaced with a Trash icon. So, does the Trash icon Delete or Archive?

After digging for far too long, I excavated the table below from the depths of the Google support site. (Spoiler: It Archives.)

Action on mobile device/client (e.g. iPhone/Outlook)	Result in Gmail on the web
Open a message	Mark a message as read
Move message to Starred	Apply a star to the message
Move a message to a folder	Apply a label to the message
Move a message to Spam	Report a message as spam
Move a message to Trash	Message will be archived.
Send a message	Store message in Sent Mail
Delete a message in inbox	Move that message to Archive
Delete a message from a folder	Remove that label from the message
Delete a message from [All Mail]	Move the message to Trash
Delete a message from Spam or Trash	Delete the message permanently

Source: http://www.google.com/support/mobile/bin/answer.py?hl=en&answer=161771