you can download the hangouts app and use a gmail address as an account. when you have internet you can make free calls to any U.S. landline.
simply choose the dial option in the app. make sure you add +1 before you dial the landline you want to call. and that's it. much better sound quality than Skype. with my 3G claro prepaid it works perfectly. (you can get one for 2.000 colones already).
vonage is a good option if you want to RECEIVE calls on a phone number that seems US based. you just need to activate the vonage app on your phone. Your phone does need to have a U.S. sim working when activating the app. otherwise you need a device connected to your home network. works good as long as you are not downloading during a call
vonage allows you to choose what area code your number will have.