Telecommuting from Spain to America everyday?? (Madrid)

Does anyone know from experience what is the best service/plan/phone provider to make calls from Spain to US numbers everyday. Due to my work, I need to figure our the best and most cost effective way of calling the US everyday from Spain. I haven't fully looked in to this but I have heard of Vonage, Magicjack etc. I need a clear line that sounds like I'm calling from a landline, not some cheap Internet line. Any insight or advice would be greatly appreciated!