iPhone Users, What Do You Do to Silence/Decline an Incoming Call?

This is not a question asking how to do it; it's a question asking how *you* do it. This is just a bit of personal research.

How long did it take you to figure out, for the first time, how to do it? Do you think this function should be made more clear to new users instead of leaving it up to them to find it by themselves as if it were an Easter egg?