Running on a out-of-box, unupgraded T-Mobile G2, which is running Froyo, if I'm correct.
This version of the Gmail application has a delete button, which is undocumented in their web help.
When I use it, it appears to delete the entire thread/conversation, rather than a single message. Is this the expected behavior?
UPDATE:
Found the verison number -> "Version 2.3"