Right!
The only way to PM is to be friends.
You can include a PM with a friend request.
Also, you can leave a note without too much detail on someone's page.
Either way, they will be notified via email.
have fun,
M
Eric's question is a great one. If you want to share your phone number or email with someone, do it in a friend request or a private message. Never post it in public for obvious reasons (that apparently are not that obvious to some). Check out the reason here.