DO not give John Mayer your number. The Grammy-winning songster ventured into "phone-stalking" territory recently when he left up to 10 messages a day on what he thought was Kanye West's cellphone, trying to talk the rapper into working with him. But the number, West's former digits, belongs to a publicist on the Left Coast. Mayer's desperation led him to create a rap for West about how great Kanye is and how much Mayer wanted to work with him. "It was hilariously bad," said a source. "The two are friends and collaborators who, yes, do leave messages for each other," confirmed Mayer's rep Ken Sunshine.