I haven't used it for calls via my computer yet, but I have used it via wifi on my android phone (you have to do a few things to get it to work over a data network instead of making a ridiculous long distance mobile call).
Greatest thing about it is being able to text my friends en los ee.uu. on my old phone (I got the number a few months before I moved, so friends could get used to it), using my prepaid data plan (350 mb/month for 35 soles), just as if I was back there.
Now if I can only get my internet sped up so I can watch things in much higher quality from the vulkano box in my parents' house...
(Just noticed I should probably update my location. Ha.)