Read through this... http://support.apple.com/kb/HT4319
When calling someone using an iPad 2, iPod touch, or FaceTime for Mac: Use the email address designated for FaceTime of the person you are calling.
For someone to FaceTime your pad, they need to call an e mail address associated with the pad. Look at settings, FaceTime, and see what was entered for your 'receive at' address. If this is the same address as your phone, the factime will try to go to both. If you want the call to go only tomyour pad, get a second e mail address and enter it in received at in the settings. Then, if someone calls that address, your pad will ring.