Best rates from Spain to the US?

[Pitch]

First off, apologies if this has been covered already. I searched but didn't find anything that answered my questions, so I hope this is fine.

Ok, so I'll be studying in Spain for the next semester (leaving Tuesday!) & have been searching for the best rates to call my parents & friends at home in America. I know Skype has really cheap rates and I do plan to make calls through it if I can, but I don't want to be tied down to my computer as I don't know if I'll have internet access in the house or where the closest place I will have it that's private. So, given that, I've been looking for different GSM SIM plans. These are the best rates I found (in US$) (aside: last summer I used Piccell):

Spain - US per min.
.38¢ Geosim (.39¢ to Spain)
.41¢ Yoigo (.17¢ to Spain)
.43¢ Globalism (.42¢ to Spain)
.58¢ Piccell - monthly (.28¢ to Spain)
.59¢ Telestial (.59 8:00-20:00/.24 20:00 - 24h/.38 24h - 8h) (.36¢ to Spain)
.60¢ Travelsim (.60¢ to Spain)

Text - nat. per txt

FREE Telestial (I think...)
.14¢ Yoigo
.26¢ Piccell
.40¢ Travelsim
.73¢ Globalism
.82¢ Geosim

Text - int. per txt

.14¢ Yoigo
.40¢ Travelsim
.41¢ Piccell
.67¢ Globalism
.73¢ Geosim
.79¢ Telestial

Given these rates, would it just be better to buy a SIM for outbound national calls (plus to receive calls) & an international calling card for US calls? If so, any recommendations for these cards and a Spanish provider? Yoigo seems cheap from the above quoted rates, but I don't exactly understand how Vodafone or Movistar's rates work, or which is the most advantageous.

Thanks for any help as well as any other advice you guys can give me (seriously, <i>any</i> advice),
Hunter, NY

[fedeprovenza]

I think Yoigo, even if it's the latest mobile's company who enterred in Spain, is the better