Skype mobile international calling?

My girlfriend lives in brazil and I spend about 200 dollars a month just in texts alone to her with my cellphone..so then we had this plan to both get phones with skype so we could both sign into skype at the same time and call eahother using 3g.and we could walk around talking on the fone as if we lived in the same city..her phone (iphone4) can make skype to skype calls with 3g but mine(droidx) says that sine I live in usa I.can only make skype calls using wifi...is there anyway to get around this? Or another program. Or app. We can use to call eschother for free with 3g?