Hi.
I´m looking at Frontier as well - for a project in Cochabamba, Bolivia.
They have some great reviews, and seem very professional in what they do.
Only thing that´s raising a doubt is the price !
Looking around, it seems you can get things arranged much cheaper by organizations ´in country´ (don´t know if that´s the same for your destination)
Try having a look at someone like Idealist.org, or GoAbroad.com
They have loads of volunteer places listed.