The standard cards are pretty good if you dont mind paying a little more. I was using Rebtel for a while and used to spend quite a bit on it. Got an email few days ago on a new card service called Dial Mama. Because of the low rates they had I decided to give a  try and it worked pretty well. The connection and quality was much better than some I used in past. Not sure how long it will last but until then I am gonna use it.www.dialmama.com