International Texting

Hi All,
does anyone have suggestions for apps for cheap international texting? Googling results in everyone recommending textplus, but it doesn't support anywhere outside of US and Canada. My girlfriend is in Tanzania and I actually have found an easy way to text her with rebtel for about 2 cents per text. I'm totally fine with that for sure and would be willing to pay up to 10 cents or so but the problem is I get charged $.20 every time she responds to me. I can't figure out a way to have her text me without getting huge charges. Any suggestions anyone? Thanks