It's like a computer dialog box. Just as users don't read dialog boxes, phone users don't listen to the message at all. They just wait until the beep and start talking. I used to have a home phone that had voice mail boxes and we had a message that said, "To leave a message for husband, press 1, to leave a message for wife press 2." It had a default mailbox if the user didn't press anything. 95% of calls went to the default mailbox. People are idiots.

You can always set your voicemail number to something funny. I used to set it to a French ski resort automated weather report telephone - that's annoying and an expensive international call to boot, so people quickly stop trying (not that you'd notice if they didn't).

AFAIK It is charged to you (to whom forwarding) not to the caller