Phone question...?

hi i bought a palm treo 700w off ebay...perfect condition..phone works great..im just having a problem...i dont know how to change the old voicemail number...the number that its calling is some weird number from another state and i have not a clue how to change it...is there any way i can do this myself?Phone question...?don't buy stuff from ebayPhone question...?does it come with a guide? try pressing 4444