If you need to make a phone call to the United States from Spain (or from anywhere), you should know that Skype allows you to make affordable international calls to mobile phones and landlines. You can pay for these calls with Skype Credit. If you make international phone calls regularly, you could contemplate making a subscription, since you would save even more money.
If what you need is to call a Spanish mobile phone or landline from Skype, you can also do that with Skype Credit or a subscription. The price you will have to pay depends always on the country you are calling to, not the country you are calling from, so to see the cost of calling to a Spanish phone number you would need to search for Spain in the link provided below.
Click here to access Skype’s website on this topic, with detailed information on how to get a subscription, Skype Credit, prices, etc.
You can also check all the different countries and their specific cost.