Why so many prayers and mantras?

Why do Buddhas, Bodhisattvas, Goddesses, Gods and all nature of Divine Beings have so many prayers and mantras of their own?

Just as we humans have several phones for people to call us, ( Cellphones where some evenhave 2 or 3, House Phones, Internet phone...and emails, Work phones etc etc ) I believe the Divine beings too have the same technique. MANTRAS and PRAYERS are what they are. If the mantra we have is the deity's PERSONAL Mantra ( Personal Handphone), chances of an immediate answer is Higher than if we "call" their General mantra ( Work Line) and leave a message. It is I believe the skillful and compassionate ways of the Divine to ensure that nomatter WHERE they are, they are 24/7 on call for us... although sometimes it takes longer for a reply... just like some of us take several days before replying emails hehehe.