I use MagicJack, I set it up with a number from the states and I can talk as much as I want to anyone in the States, (umm i think P.R. and Canada are free too), for only 20 $USD a year.
The quality is excellent (if im not downloading anything or surfing the internet because if the crappy internet here, well in my town at least).
For best results make sure your computer has USB 2.0, which is pretty standard nowadays but Ive been surprised with the computers ive seen here lol!
Also another nifty thing is, that you can call other magicjack owners in the country for free also. So the telephone company's highway robbery racket is pretty much nullified with this baby!