Hello, I am also a new macbook user! I had the same issues as you when I first started using face time. My issue was that the device I was trying to make calls to wasn't on wi-fi. It was some glitch that you can't use it over 3G. Try letting the other user know that the need to connect to wifi if the have an ipod/iphone/ipad/ipod touch. If this isn't the issue, sorry I couldn't be of more help!