I purchased some credit from lowratevoip to call abroad, they offer free service to call few countries and charge for others. I spent half of my credit in 2 days and i got 30 days free charges for some countries. but i found their service is absolutely useless because of my rest credit is gone and there is no free call ... and also i'm wondring why some friends of mine got 30 days free charge to call few countries and thier rest of credit never gone