iphone 4 no invitees or availablity HELP!!!

My iphone 4 doesnt have invitees and availablity on iCal, but my friend who has the same phone, we got it at the same time, and use the same computer has her invitees and availability on her ical. Why isnt mine there? She uses yahoo and i have gmail and our computer is a macbook. PLEASE HELP!!!!